CN116708777A

CN116708777A - Image encoding/decoding method and apparatus, and recording medium storing bit stream

Info

Publication number: CN116708777A
Application number: CN202310765419.5A
Authority: CN
Inventors: 李镇浩; 林成昶; 姜晶媛; 高玄硕; 全东山; 李河贤; 赵承眩; 金晖容; 崔振秀
Original assignee: Electronics and Telecommunications Research Institute ETRI
Current assignee: Electronics and Telecommunications Research Institute ETRI
Priority date: 2016-07-18
Filing date: 2017-07-17
Publication date: 2023-09-05
Also published as: US20190222837A1; US11368681B2; US11882272B2; CN116708774A; JP2019525577A; KR20230150921A; WO2018016823A1; CN109479129A; US20240048693A1; CN116708776A; KR20180009318A; JP2022191450A; CN116708773A; CN116708775A; CN109479129B; US20220279171A1; KR20210134553A

Abstract

The present application relates to an image encoding/decoding method and apparatus and a recording medium storing a bitstream. The image decoding method for performing intra prediction according to the present application may include the steps of: dividing the current block into at least one sub-block; deriving an intra prediction mode for the at least one sub-block; constructing a reference sample point for intra-frame prediction; and performing intra prediction for the at least one sub-block based on the derived intra prediction mode.

Description

Image encoding/decoding method and apparatus, and recording medium storing bit stream

The present application is a divisional application of patent application entitled "image encoding/decoding method and apparatus and recording medium storing bit stream", having application date of 2017, 7, 17, and application number of 201780044916.9.

Technical Field

The present application relates to a method and apparatus for encoding/decoding an image. In particular, the present application relates to a method and apparatus for encoding/decoding an image using intra prediction and a recording medium storing a bitstream generated by the image encoding method/apparatus of the present application.

Background

Recently, demands for high resolution and high quality images such as High Definition (HD) images and Ultra High Definition (UHD) images have been growing in various application fields. However, the data amount of higher resolution and quality image data is increased as compared with conventional image data. Accordingly, when image data is transmitted by using a medium such as a conventional wired broadband network and a wireless broadband network, or when image data is stored by using a conventional storage medium, the cost of transmission and storage increases. In order to solve these problems that occur with the increase in resolution and quality of image data, efficient image encoding/decoding techniques are required for higher resolution and higher quality images.

Image compression techniques include various techniques including: inter prediction techniques that predict pixel values included in a current picture from a previous picture or a subsequent picture of the current picture; an intra prediction technique of predicting a pixel value included in a current picture by using pixel information in the current picture; transform and quantization techniques for compressing the energy of the residual signal; entropy coding techniques that assign short codes to high frequency of occurrence values and long codes to low frequency of occurrence values; etc. By using such an image compression technique, image data can be efficiently compressed and can be transmitted or stored.

Disclosure of Invention

Technical problem

It is an object of the present invention to provide a method and apparatus for encoding and decoding video images to improve compression efficiency.

Another object of the present invention is to provide a method and apparatus for encoding and decoding a video image using intra prediction to improve compression, and to provide a recording medium storing a bitstream generated by the image encoding method/apparatus of the present invention.

Solution scheme

The image decoding method for performing intra prediction according to the present invention may include: dividing the current block into at least one sub-block; deriving an intra prediction mode for the at least one sub-block; constructing a reference sample point for intra-frame prediction; and performing intra prediction for the at least one sub-block based on the derived intra prediction mode.

In the method for decoding an image according to the present invention, the dividing step may be performed if the size of the current block corresponds to a predetermined size.

In the method for decoding an image according to the present invention, if the horizontal length or the vertical length of the current block is a length that can be divided, division may be performed.

In the method for decoding an image according to the present invention, the at least one sub-block may have a predetermined size or shape.

In the method for decoding an image according to the present invention, the division may be performed based on division information about the current block.

In the method for decoding an image according to the present invention, the derivation of the prediction mode for the at least one sub-block may be performed based on at least one intra prediction mode of the current block and the intra prediction modes of at least one neighboring block.

In the method for decoding an image according to the present invention, the intra prediction mode for the at least one sub-block may be derived as a statistical value of the intra prediction modes of the at least one neighboring block, and the statistical value may be at least one of a minimum value, a maximum value, a most frequent value, a median value, a mean value, and a weighted mean value.

In the method for decoding an image according to the present invention, an intra prediction mode for the at least one sub-block may be derived based on a size of the at least one neighboring block.

In the method for decoding an image according to the present invention, an intra prediction mode for the at least one sub-block may be derived based on directionality of the intra prediction mode of the at least one neighboring block.

In the method for decoding an image according to the present invention, an intra prediction mode of the current block may be derived using a Most Probable Mode (MPM), and an intra prediction mode for the at least one sub-block may be derived based on a comparison result between the intra prediction mode of the at least one neighboring block and the intra prediction mode of the current block.

In the method for decoding an image according to the present invention, the construction of the reference sample points may be performed using at least one reconstructed sample line.

In the method for decoding an image according to the present invention, the construction of the reference sample points may be performed by calculating a weighted mean of at least one reconstructed sample point included in the at least one reconstructed sample point line.

In the method for decoding an image according to the present invention, the weight for calculating the weighted mean may be determined based on the distance from the current block.

In the method for decoding an image according to the present invention, as the distance from the current block becomes smaller, the weight for calculating the weighted average may become larger.

In the method for decoding an image according to the present invention, the number of the at least one reconstructed sample line may be determined based on at least one of a size, a shape, and an intra prediction mode of the current block.

An image encoding method for performing intra prediction according to the present invention may include: dividing the current block into at least one sub-block; determining an intra prediction mode for the at least one sub-block; constructing a reference sample point for intra-frame prediction; and performing intra prediction for the at least one sub-block based on the determined intra prediction mode.

A recording medium storing a bitstream generated by an image encoding method for performing intra prediction may store the bitstream generated by the image encoding method, wherein the image encoding method includes: dividing the current block into at least one sub-block; determining an intra prediction mode for the at least one sub-block; constructing a reference sample point for intra-frame prediction; and performing intra prediction for the at least one sub-block based on the determined prediction mode.

An image decoding apparatus for performing intra prediction may include an intra prediction unit, wherein the intra prediction unit performs the following operations: dividing the current block into at least one sub-block; deriving an intra prediction mode for the at least one sub-block; constructing a reference sample point for intra-frame prediction; and performing intra prediction for the at least one sub-block based on the derived intra prediction mode.

An image encoding apparatus for performing intra prediction may include an intra prediction unit, wherein the intra prediction unit performs: dividing the current block into at least one sub-block; determining an intra prediction mode for the at least one sub-block; constructing a reference sample point for intra-frame prediction; and performing intra prediction for the at least one sub-block based on the determined intra prediction mode.

Advantageous effects

According to the present invention, an image encoding/decoding method and apparatus for improving compression efficiency can be provided.

According to the present invention, it is possible to provide an image encoding/decoding method and apparatus using intra prediction, which improves compression efficiency, and a recording medium storing a bitstream generated by the image encoding method/apparatus of the present invention.

Drawings

Fig. 1 is a block diagram showing a configuration of an encoding apparatus according to an embodiment of the present invention.

Fig. 2 is a block diagram showing a configuration of a decoding apparatus according to an embodiment of the present invention.

Fig. 3 is a diagram schematically showing a partition structure of an image when the image is encoded and decoded.

Fig. 4 is a diagram illustrating a form of a Prediction Unit (PU) that may be included in a Coding Unit (CU).

Fig. 5 is a diagram illustrating a form of a Transform Unit (TU) that may be included in a Coding Unit (CU).

Fig. 6 is a diagram for explaining an embodiment of a process of intra prediction.

Fig. 7 is a diagram for explaining an embodiment of a process of inter prediction.

Fig. 8 is a diagram for explaining a transform set according to an intra prediction mode.

Fig. 9 is a diagram for explaining the processing of the transformation.

Fig. 10 is a diagram for explaining scanning of quantized transform coefficients.

Fig. 11 is a diagram for explaining block partitioning.

Fig. 12 is a diagram depicting a method of performing intra prediction on a current block according to an embodiment of the present invention.

Fig. 13 is a diagram depicting a method for deriving an intra prediction mode of a current block from neighboring blocks.

Fig. 14 is a diagram depicting an embodiment of deriving an intra prediction mode of each of one or more sub-blocks into which a current block is divided.

Fig. 15 is a diagram depicting an embodiment in which a current block is divided into sub-blocks.

Fig. 16 is a diagram depicting another embodiment of dividing a current block into sub-blocks.

Fig. 17 is a diagram depicting another embodiment of dividing a current block into sub-blocks.

Fig. 18 is a diagram depicting another embodiment of dividing a current block into sub-blocks.

Fig. 19 is an exemplary diagram depicting neighboring reconstructed sample lines that may be used for intra prediction of a current block.

Fig. 20 is a diagram depicting a method of replacing unavailable reconstructed samples with available reconstructed samples.

Fig. 21 is an exemplary diagram showing various two-dimensional filter shapes.

Fig. 22 is a diagram depicting a directional intra-prediction mode and a sample-by-sample directional intra-prediction mode.

FIG. 23 is a diagram depicting a slave P _ref Generating a 1D reference sample array p _1,ref Is a diagram of an embodiment of (a).

FIG. 24 is a diagram depicting an embodiment using reference samples at different angles depending on the location of the samples in the prediction block.

FIG. 25 is a diagram depicting an embodiment in which upper and/or left reference sample lines are used to reconstruct a respective block.

Fig. 26 is a diagram depicting an embodiment of a corresponding block of a first color component reconstructed in the case where the size of a second color component prediction target block is 4×4.

Fig. 27 is an exemplary diagram depicting a sample of a first color component and a sample of a second color component.

Detailed Description

Many modifications may be made to the present invention and there are various embodiments of the present invention, examples of which will now be provided with reference to the accompanying drawings and described in detail. However, the present invention is not limited thereto, and although the exemplary embodiments may be construed to include all modifications, equivalents, or alternatives falling within the technical spirit and scope of the present invention. Like reference numerals refer to the same or similar functionality in all respects. In the drawings, the shape and size of elements may be exaggerated for clarity. In the following detailed description of the invention, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure. It is to be understood that the various embodiments of the disclosure, although different, are not necessarily mutually exclusive. For example, the particular features, structures, and characteristics described herein in connection with one embodiment may be implemented in other embodiments without departing from the spirit and scope of the disclosure. Further, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the disclosure. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled.

The terms "first," "second," and the like, as used in the specification, may be used to describe various components, but these components are not to be construed as limiting the terms. The term is used merely to distinguish one component from another. For example, a "first" component may be termed a "second" component, and a "second" component may be similarly termed a "first" component, without departing from the scope of the present invention. The term "and/or" includes a combination of items or any of a plurality of items.

It will be understood that in the present specification, when an element is referred to simply as being "connected" or "coupled" to another element, it can be "directly connected" or "directly coupled" to the other element or be connected or coupled to the other element with other elements interposed therebetween. In contrast, it will be understood that when an element is referred to as being "directly coupled" or "directly connected" to another element, there are no intervening elements present.

Further, constituent elements shown in the embodiments of the present invention are independently shown so as to exhibit characteristic functions different from each other. Therefore, this does not mean that each constituent element is composed in a separate constituent unit of hardware or software. In other words, for convenience, each component includes each of the enumerated components. Thus, at least two of each component may be combined to form one component, or one component may be divided into a plurality of components to perform each function. Embodiments in which each component is combined and embodiments in which one component is divided are also included in the scope of the present invention without departing from the essence of the present invention.

The terminology used in the description presented herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The use of the expression in the singular includes the plural unless it has a distinct meaning in context. In this specification, it will be understood that terms, such as "comprises," "comprising," "has," "having," "includes," etc., are intended to specify the presence of stated features, amounts, steps, acts, elements, components, or combinations thereof disclosed in the specification, but are not intended to preclude the possibility that one or more other features, amounts, steps, acts, elements, components, or combinations thereof may be present or added. In other words, when a specific element is referred to as being "included", elements other than the corresponding element are not excluded, and additional elements may be included in the embodiments of the present invention or be within the scope of the present invention.

Furthermore, some constituent elements may not be indispensable constituent elements performing the necessary functions of the present invention, but may be optional constituent elements merely improving the performance thereof. The present invention can be implemented by including only essential constituent elements for implementing the essence of the present invention, excluding constituent elements used in enhancing performance. Structures that include only the indispensable components and exclude optional components that are used in merely enhancing performance are also included in the scope of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing exemplary embodiments of the present invention, well-known functions or constructions will not be described in detail since they would unnecessarily obscure the present invention. The same constituent elements in the drawings are denoted by the same reference numerals, and repetitive description of the same elements will be omitted.

Further, hereinafter, an image may mean a picture constituting a video, or may mean a video itself. For example, "encoding or decoding or both" may mean "encoding or decoding or both" a video, and may mean "encoding or decoding or both one image among a plurality of images of a video. Here, the picture and the image may have the same meaning.

Description of the terms

An encoder: may mean a device that performs the encoding.

A decoder: it may mean a device performing decoding.

Analysis: the value of the syntax element may be defined by performing entropy decoding, or the entropy decoding itself may be defined.

And (3) block: it may mean the samples of an mxn matrix. Here, M and N are positive integers, and a block may mean a sample matrix in two dimensions.

Sampling points: is the basic unit of a block and can indicate a range of 0 to 2 depending on the bit depth (Bd) ^Bd -1. A sample may mean a pixel in the present invention.

A unit: it may mean a unit of encoding and decoding an image. In encoding and decoding an image, a unit may be an area generated by partitioning one image. Further, a unit may mean a sub-division unit when one image is partitioned into a plurality of sub-division units during encoding or decoding. When encoding and decoding an image, predetermined processing for each unit may be performed. A cell may be partitioned into sub-cells that are smaller in size than the cell. Units may mean blocks, macro blocks, coding tree units, coding tree blocks, coding units, coding blocks, prediction units, prediction blocks, transform units, transform blocks, etc. in terms of function. Further, to distinguish a cell from a block, the cell may include a luminance component block, a chrominance component block of the luminance component block, and a syntax element of each color component block. The cells may have various sizes and shapes, in particular, the shape of the cells may be a two-dimensional geometry, such as rectangular, square, trapezoidal, triangular, pentagonal, etc. Further, the unit information may include at least one of a unit type (indicating an encoding unit, a prediction unit, a transformation unit, etc.), a unit size, a unit depth, an order in which the units are encoded and decoded, and the like.

Reconstructing neighboring units: it may mean a reconstruction unit that is previously encoded or decoded spatially/temporally, and the reconstruction unit is adjacent to the encoding/decoding target unit. Here, reconstructing a neighboring unit may mean reconstructing a neighboring block.

Adjacent blocks: may mean a block adjacent to the encoding/decoding target block. The block adjacent to the encoding/decoding target block may mean a block having a boundary in contact with the encoding/decoding target block. Neighboring blocks may mean blocks located at neighboring vertices of the encoding/decoding target block. Neighboring blocks may mean reconstructing neighboring blocks.

Cell depth: the degree to which a cell is partitioned may be intended. In the tree structure, the root node may be the highest node and the leaf node may be the lowest node.

The symbols: it may mean that syntax elements of the target unit for encoding/decoding, encoding parameters, values of transform coefficients, and the like.

Parameter set: header information in the structure of the bitstream may be intended. The parameter sets may comprise at least one parameter set of a video parameter set, a sequence parameter set, a picture parameter set or an adaptive parameter set. Further, the parameter set may mean stripe header information, parallel block (tile) header information, and the like.

Bit stream: may mean a bit string including encoded image information.

Prediction unit: it may mean a basic unit when inter prediction or intra prediction is performed and compensation for the prediction. One prediction unit may be partitioned into a plurality of partitions. In this case, each partition of the plurality of partitions may be a basic unit in performing prediction and compensation, and each partition obtained from the prediction unit partition may be a prediction unit. Furthermore, one prediction unit may be partitioned into a plurality of small prediction units. The prediction unit may have various sizes and shapes, and in particular, the shape of the prediction unit may be a two-dimensional geometric figure such as a rectangle, a square, a trapezoid, a triangle, a pentagon, and the like.

Prediction unit partitioning: may mean the shape of the partitioned prediction unit.

Reference picture list: it may mean a list including at least one reference picture, wherein the at least one reference picture is used for inter prediction or motion compensation. The type of the reference picture List may be List Combined (LC), list 0 (L0), list 1 (L1), list 2 (L2), list 3 (L3), or the like. At least one reference picture list may be used for inter prediction.

Inter prediction indicator: it may mean one of the following: inter prediction direction (unidirectional prediction, bidirectional prediction, etc.) of an encoding/decoding target block in the case of inter prediction, the number of reference pictures used to generate a prediction block by the encoding/decoding target block, and the number of reference blocks used to perform inter prediction or motion compensation by the encoding/decoding target block.

Reference picture index: may mean an index of a particular reference picture in the reference picture list.

Reference picture: it may mean a picture that a particular unit refers to for inter prediction or motion compensation. The reference picture may be referred to as a reference picture.

Motion vector: is a two-dimensional vector for inter prediction or motion compensation, and may mean an offset between an encoding/decoding target picture and a reference picture. For example, (mvX, mvY) may indicate a motion vector, mvX may indicate a horizontal component, and mvY may indicate a vertical component.

Motion vector candidates: it may mean a unit that becomes a prediction candidate when predicting a motion vector, or may mean a motion vector of the unit.

Motion vector candidate list: it may mean a list configured by using motion vector candidates.

Motion vector candidate index: may mean an indicator indicating a motion vector candidate in the motion vector candidate list. The motion vector candidate index may be referred to as an index of a motion vector predictor.

Motion information: it may mean a motion vector, a reference picture index, and an inter prediction indicator, and information including at least one of reference picture list information, a reference picture, a motion vector candidate index, and the like.

Merging candidate list: it may mean a list configured by using merge candidates.

Combining candidates: spatial merge candidates, temporal merge candidates, combined bi-predictive merge candidates, zero merge candidates, etc. may be included. The merge candidates may include motion information such as prediction type information, reference picture indexes for each list, motion vectors, and the like.

Merging index: may mean information indicating a merge candidate in the merge candidate list. Further, the merge index may indicate a block of derived merge candidates among reconstructed blocks spatially/temporally adjacent to the current block. Further, the merge index may indicate at least one of a plurality of pieces of motion information of the merge candidate.

A conversion unit: it may mean a basic unit when encoding/decoding similar to transforming, inverse transforming, quantizing, inverse quantizing, and transform coefficient encoding/decoding is performed on the residual signal. One transform unit may be partitioned into multiple small transform units. The transformation unit may have various sizes and shapes. In particular, the shape of the transformation unit may be a two-dimensional geometry, such as a rectangle, square, trapezoid, triangle, pentagon, etc.

Scaling: it may mean a process of multiplying a factor by the transform coefficient level, as a result of which the transform coefficient may be generated. Scaling may also be referred to as dequantization.

Quantization parameters: may mean values used in scaling the transform coefficient levels during quantization and dequantization. Here, the quantization parameter may be a value mapped to a quantized step size.

Delta (Delta) quantization parameter: it may mean a difference between a quantization parameter of the encoding/decoding target unit and a predicted quantization parameter.

Scanning: it may mean a method of ordering the order of coefficients within a block or matrix. For example, the operation of ordering a two-dimensional matrix into a one-dimensional matrix may be referred to as scanning, and the operation of ordering a one-dimensional matrix into a two-dimensional matrix may be referred to as scanning or inverse scanning.

Transform coefficients: may mean coefficient values generated after performing the transformation. In the present invention, the quantized transform coefficient level (i.e., the transform coefficient to which quantization is applied) may be referred to as a transform coefficient.

Non-zero transform coefficients: a transform coefficient having a value other than 0 may be intended, or a transform coefficient level having a value other than 0 may be intended.

Quantization matrix: it may mean a matrix used in quantization and inverse quantization in order to improve the subject quality (subject quality) or object quality (subject quality) of an image. The quantization matrix may be referred to as a scaling list.

Quantization matrix coefficients: each element of the quantization matrix may be implied. The quantized matrix coefficients may be referred to as matrix coefficients.

Default matrix: it may mean a predetermined quantization matrix that is predefined in the encoder and decoder.

Non-default matrix: it may mean a quantization matrix transmitted/received by a user without being predefined in the encoder and decoder.

Coding tree unit: may be formed of one luma component (Y) coding tree unit and associated two chroma component (Cb, cr) coding tree units. Each coding tree unit may be partitioned using at least one partitioning method (such as a quadtree, binary tree, etc.) to constitute sub-units such as coding units, prediction units, transform units, etc. The coding tree unit may be used as a term for indicating a block of pixels, i.e. a processing unit in a decoding/encoding process of an image, such as a partition of an input image.

Coding tree blocks: may be used as a term for indicating one of a Y coding tree unit, a Cb coding tree unit, and a Cr coding tree unit.

The encoding apparatus 100 may be a video encoding apparatus or an image encoding apparatus. The video may include one or more images. The encoding apparatus 100 may encode the one or more images of the video in a temporal order.

Referring to fig. 1, the encoding apparatus 100 may include a motion prediction unit 111, a motion compensation unit 112, an intra prediction unit 120, a switcher 115, a subtractor 125, a transform unit 130, a quantization unit 140, an entropy encoding unit 150, an inverse quantization unit 160, an inverse transform unit 170, an adder 175, a filter unit 180, and a reference picture buffer 190.

The encoding apparatus 100 may encode the input picture in an intra mode or an inter mode or both the intra mode and the inter mode. Further, the encoding apparatus 100 may generate a bitstream by encoding an input picture, and may output the generated bitstream. When the intra mode is used as the prediction mode, the switcher 115 can switch to intra. When the inter mode is used as the prediction mode, the switcher 115 may switch to the inter mode. Here, the intra mode may be referred to as an intra prediction mode, and the inter mode may be referred to as an inter prediction mode. The encoding apparatus 100 may generate a prediction block of an input picture. Further, after generating the prediction block, the encoding apparatus 100 may encode a residual between the input block and the prediction block. The input picture may be referred to as a current image that is a target of current encoding. The input block may be referred to as a current block or may be referred to as an encoding target block that is a target of current encoding.

When the prediction mode is an intra mode, the intra prediction unit 120 may use a pixel value of a previously encoded block adjacent to the current block as a reference pixel. The intra prediction unit 120 may perform spatial prediction by using the reference pixels, and may generate prediction samples of the input block by using the spatial prediction. Here, intra prediction may mean intra frame prediction.

When the prediction mode is an inter mode, the motion prediction unit 111 may search for a region optimally matching the input block from the reference picture in the motion prediction process, and may derive a motion vector by using the searched region. The reference picture may be stored in a reference picture buffer 190.

The motion compensation unit 112 may generate a prediction block by performing motion compensation using the motion vector. Here, the motion vector may be a two-dimensional vector for inter prediction. Further, the motion vector may indicate an offset between the current picture and the reference picture. Here, the inter prediction may mean inter frame prediction.

When the value of the motion vector is not an integer, the motion prediction unit 111 and the motion compensation unit 112 may generate a prediction block by applying an interpolation filter to a partial region in the reference picture. In order to perform inter prediction or motion compensation based on the coding unit, which method is used for a motion prediction and compensation method of a prediction unit in the coding unit may be determined among a skip mode, a merge mode, an AMVP mode, and a current picture reference mode. Inter prediction or motion compensation may be performed according to each mode. Here, the current picture reference mode may mean a prediction mode using a previously reconstructed region of the current picture having the encoding target block. In order to indicate the pre-reconstructed region, a motion vector for the current picture reference mode may be defined. Whether or not to encode the encoding target block in the current picture reference mode may be encoded by using the reference picture index of the encoding target block.

The subtractor 125 may generate a residual block by using a residual between the input block and the prediction block. The residual block may be referred to as a residual signal.

The transform unit 130 may generate transform coefficients by transforming the residual block, and may output the transform coefficients. Here, the transform coefficient may be a coefficient value generated by transforming the residual block. In the transform skip mode, the transform unit 130 may skip the transform of the residual block.

Quantized transform coefficient levels may be generated by applying quantization to transform coefficients. Hereinafter, in an embodiment of the present invention, the quantized transform coefficient level may be referred to as a transform coefficient.

The quantization unit 140 may generate quantized transform coefficient levels by quantizing the transform coefficients according to quantization parameters, and may output the quantized transform coefficient levels. Here, the quantization unit 140 may quantize the transform coefficient by using a quantization matrix.

The entropy encoding unit 150 may generate a bitstream by performing entropy encoding on the values calculated by the quantization unit 140 or on the encoding parameter values calculated in the encoding process, etc., according to the probability distribution, and may output the generated bitstream. The entropy encoding unit 150 may perform entropy encoding on information for decoding an image and entropy encoding on information of pixels of the image. For example, the information for decoding the image may include syntax elements or the like.

When entropy encoding is applied, symbols are represented by allocating a small number of bits to symbols having a high occurrence probability and allocating a large number of bits to symbols having a low occurrence probability, thereby reducing the size of a bitstream encoding a target symbol. Therefore, the compression performance of image coding can be improved by entropy coding. For entropy encoding, the entropy encoding unit 150 may use an encoding method such as exponential golomb, context Adaptive Variable Length Coding (CAVLC), and Context Adaptive Binary Arithmetic Coding (CABAC). For example, the entropy encoding unit 150 may perform entropy encoding by using a variable length coding/coding (VLC) table. Further, the entropy encoding unit 150 may derive a binarization method of the target symbol and a probability model of the target symbol/binary bit, and then may perform arithmetic encoding by using the derived binarization method or the derived probability model.

In order to encode the transform coefficient levels, the entropy encoding unit 150 may change coefficients in the form of a two-dimensional block into a one-dimensional vector form by using a transform coefficient scanning method. For example, coefficients in two dimensions may be changed to one-dimensional vectors by scanning the coefficients of the block with an upper right scan. Depending on the size of the transform unit and the intra prediction mode, a vertical direction scan for scanning coefficients in the form of a two-dimensional block in the column direction and a horizontal direction scan for scanning coefficients in the form of a two-dimensional block in the row direction may be used instead of using an upper right scan. That is, depending on the size of the transform unit and the intra prediction mode, it may be determined which scan method among the upper right scan, the vertical direction scan, and the horizontal direction scan is to be used.

The encoding parameters may include information such as syntax elements encoded by an encoder and transmitted to a decoder, and may include information that may be derived in an encoding or decoding process. The encoding parameter may mean information necessary to encode or decode an image. For example, the encoding parameters may include at least one value or combination of the following: block size, block depth, block partition information, unit size, unit depth, unit partition information, partition flag in quadtree form, partition flag in binary tree form, partition direction in binary tree form, intra prediction mode, intra prediction direction, reference sample filtering method, prediction block boundary filtering method, filter tap, filter coefficient, inter prediction mode, motion information, motion vector, reference picture index, inter prediction direction, inter prediction indicator, reference picture list, motion vector predictor, motion vector candidate list, information on whether motion merge mode is used, motion merge candidate list, information on whether skip mode is used, interpolation filter type, motion vector size, motion vector accuracy of motion vector representation, type of transform, size of transform, information on whether additional (secondary) transforms are used, information on whether residual signals are present, coding block patterns, coding block flags, quantization parameters, quantization matrices, filter information in loops, information on whether filters are applied in loops, filter coefficients in loops, binarization/anti-binarization methods, context models, context binary bits, bypass binary bits, transform coefficients, transform coefficient levels, transform coefficient level scanning methods, image display/output order, stripe identification information, stripe types, stripe partition information, parallel block identification information, parallel block types, parallel block partition information, picture types, bit depths, and information of luminance signals or chrominance signals.

The residual signal may mean the difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming a difference between the original signal and the predicted signal. Alternatively, the residual signal may be a signal generated by transforming and quantizing a difference between the original signal and the predicted signal. The residual block may be a residual signal of a block unit.

When the encoding apparatus 100 performs encoding by using inter prediction. The encoded current picture may be used as a reference picture for another image to be subsequently processed. Accordingly, the encoding apparatus 100 may decode the encoded current picture and may store the decoded image as a reference picture. To perform decoding, inverse quantization and inverse transformation may be performed on the encoded current picture.

The quantized coefficients may be dequantized by the dequantization unit 160 and may be inverse transformed by the inverse transformation unit 170. The inverse quantized and inverse transformed coefficients may be added to the prediction block by adder 175, whereby a reconstructed block may be generated.

The reconstructed block may pass through a filter unit 180. The filter unit 180 may apply at least one of a deblocking filter, a Sample Adaptive Offset (SAO), and an Adaptive Loop Filter (ALF) to the reconstructed block or the reconstructed picture. The filter unit 180 may be referred to as a loop filter.

The deblocking filter may remove block distortion occurring at boundaries between blocks. To determine whether the deblocking filter is operated, whether the deblocking filter is applied to the current block may be determined based on pixels included in several rows or columns in the block. When a deblocking filter is applied to a block, a strong filter or a weak filter may be applied depending on the required deblocking filter strength. Further, when the deblocking filter is applied, horizontal direction filtering and vertical direction filtering can be processed in parallel.

The sample adaptive offset may add an optimal offset value to the pixel value in order to compensate for the coding error. The sample adaptive offset may correct an offset between the deblocking filtered image and the original picture for each pixel. In order to perform offset correction on a specific screen, a method of applying offset in consideration of edge information of each pixel may be used, or the following method may be used: the pixels of the image are partitioned into a predetermined number of areas, an area to be subjected to offset correction is determined, and offset correction is applied to the determined area.

The adaptive loop filter may perform filtering based on a value obtained by comparing the reconstructed picture with the original picture. Pixels of the image may be partitioned into predetermined groups, one filter applied to each group is determined, and different filtering may be performed at each group. Information about whether the adaptive loop filter is applied to the luminance signal may be transmitted for each Coding Unit (CU). The shape and filter coefficients of the adaptive loop filter applied to each block may vary. Furthermore, an adaptive loop filter having the same form (fixed form) may be applied regardless of the characteristics of the target block.

The reconstructed block that passes through the filter unit 180 may be stored in a reference picture buffer 190.

The decoding apparatus 200 may be a video decoding apparatus or an image decoding apparatus.

Referring to fig. 2, the decoding apparatus 200 may include an entropy decoding unit 210, an inverse quantization unit 220, an inverse transform unit 230, an intra prediction unit 240, a motion compensation unit 250, an adder 255, a filter unit 260, and a reference picture buffer 270.

The decoding apparatus 200 may receive the bit stream output from the encoding apparatus 100. The decoding apparatus 200 may decode the bitstream in an intra mode or an inter mode. In addition, the decoding apparatus 100 may generate a reconstructed picture by performing decoding, and may output the reconstructed picture.

When the prediction mode used in decoding is an intra mode, the switcher may be switched into the intra mode. When the prediction mode used in decoding is an inter mode, the switcher may be switched to an inter mode.

The decoding apparatus 200 may obtain a reconstructed residual block from an input bitstream and may generate a prediction block. When the reconstructed residual block and the prediction block are obtained, the decoding apparatus 200 may generate a reconstructed block as a decoding target block by adding the reconstructed residual block and the prediction block. The decoding target block may be referred to as a current block.

The entropy decoding unit 210 may generate symbols by performing entropy decoding on the bitstream according to the probability distribution. The generated symbols may include symbols having quantized transform coefficient levels. Here, the method of entropy decoding may be similar to the method of entropy encoding described above. For example, the method of entropy decoding may be the inverse of the method of entropy encoding described above.

In order to decode the transform coefficient levels, the entropy decoding unit 210 may perform transform coefficient scanning, whereby coefficients in the form of one-dimensional vectors may be changed to the form of two-dimensional blocks. For example, coefficients in the form of one-dimensional vectors may be changed to the form of two-dimensional blocks by scanning the coefficients of the blocks with an upper right scan. Depending on the size of the transform unit and the intra prediction mode, vertical direction scanning as well as horizontal direction scanning may be used instead of upper right scanning. That is, depending on the size of the transform unit and the intra prediction mode, it is possible to determine which scanning method among the upper right scanning, the vertical direction scanning, and the horizontal direction scanning is used.

The quantized transform coefficient levels may be dequantized by the dequantization unit 220 and may be inverse transformed by the inverse transform unit 230. The quantized transform coefficient levels are dequantized and inverse transformed to produce a reconstructed residual block. Here, the inverse quantization unit 220 may apply a quantization matrix to the quantized transform coefficient level.

When the intra mode is used, the intra prediction unit 240 may generate a prediction block by performing spatial prediction using pixel values of a previously decoded block adjacent to the decoding target block.

When the inter mode is used, the motion compensation unit 250 may generate a prediction block by performing motion compensation using both the reference picture stored in the reference picture buffer 270 and the motion vector. When the value of the motion vector is not an integer, the motion compensation unit 250 may generate a prediction block by applying an interpolation filter to a partial region in the reference picture. In order to perform motion compensation, based on the coding unit, which method is used for a motion compensation method of a prediction unit in the coding unit may be determined among a skip mode, a merge mode, an AMVP mode, and a current picture reference mode. Furthermore, motion compensation may be performed according to the mode. Here, the current picture reference mode may mean a prediction mode using a previously reconstructed region within the current picture having the decoding target block. The previously reconstructed region may not be adjacent to the decoding target block. To indicate the previously reconstructed region, a fixed vector may be used for the current picture reference mode. In addition, a flag or index indicating whether the decoding target block is a block encoded in the current picture reference mode may be signaled and may be obtained by using the reference picture index of the decoding target block. The current picture for the current picture reference mode may exist at a fixed position (e.g., a position with reference picture index 0 or a last position) within the reference picture list for the decoding target block. Further, the current picture may be variably located within the reference picture list, for which a reference picture index indicating a position of the current picture may be signaled. Here, signaling a flag or index may mean: the encoder entropy encodes and includes the respective flag or index into the bitstream, and the decoder entropy decodes the respective flag or index from the bitstream.

The reconstructed residual block may be added to the prediction block by adder 255. The block generated by adding the reconstructed residual block and the prediction block may pass through the filter unit 260. The filter unit 260 may apply at least one of a deblocking filter, a sample adaptive offset, and an adaptive loop filter to the reconstructed block or the reconstructed picture. The filter unit 260 may output the reconstructed picture. The reconstructed picture may be stored in a reference picture buffer 270 and may be used for inter prediction.

Fig. 3 is a diagram schematically showing a partition structure of an image when the image is encoded and decoded. Fig. 3 schematically shows an embodiment of partitioning a unit into a plurality of sub-units.

For efficient partitioning of images, coding Units (CUs) may be used in encoding and decoding. Here, the encoding unit may mean a unit for encoding, and the unit may be a combination of 1) a syntax element and 2) a block including image samples. For example, "partition of a unit" may mean "partition of a block associated with a unit". The block partition information may include information about the depth of the unit. The depth information may indicate the number of times a unit is partitioned or the degree to which the unit is partitioned, or both.

Referring to fig. 3, an image 300 is sequentially partitioned for each Largest Coding Unit (LCU), and a partition structure is determined for each LCU. Here, LCU and Coding Tree Unit (CTU) have the same meaning. One unit may have depth information based on a tree structure and may be hierarchically partitioned. Each partitioned subunit may have depth information. The depth information indicates the number of times the unit is partitioned or the degree to which the unit is partitioned, or both, and thus, the depth information may include information about the size of the sub-unit.

The partition structure may mean a distribution of Coding Units (CUs) in LCU 310. A CU may be a unit for efficiently encoding/decoding an image. The distribution may be determined based on whether a CU is to be partitioned multiple times (a positive integer equal to or greater than 2, including 2, 4, 8, 16, etc.). The width dimension and the height dimension of the partitioned CU may be a half width dimension and a half height dimension of the original CU, respectively. Alternatively, the width and height dimensions of the partitioned CUs may be smaller than the width and height dimensions of the original CUs, respectively, depending on the number of partitions. The partitioned CU may be recursively partitioned into a plurality of further partitioned CUs, wherein the further partitioned CUs have smaller width and height dimensions than the partitioned CUs' width and height dimensions according to the same partitioning method.

Here, the partitioning of the CU may be recursively performed up to a predetermined depth. The depth information may be information indicating the size of the CU, and may be stored in each CU. For example, the depth of the LCU may be 0, and the depth of the minimum coding unit (SCU) may be a predetermined maximum depth. Here, the LCU may be a coding unit having the above-described maximum size, and the SCU may be a coding unit having the minimum size.

Whenever LCU 310 starts to be partitioned and the width and height dimensions of the CU are reduced by the partitioning operation, the depth of the CU increases by 1. In the case of CUs that cannot be partitioned, the CU may have a size of 2n×2n for each depth. In the case of CUs that can be partitioned, a CU having a size of 2n×2n may be partitioned into a plurality of n×n sized CUs. The size of N is halved each time the depth increases by 1.

For example, when one coding unit is partitioned into four sub-coding units, the width dimension and the height dimension of one of the four sub-coding units may be half the width dimension and half the height dimension of the original coding unit, respectively. For example, when a coding unit of a size of 32×32 is partitioned into four sub-coding units, each of the four sub-coding units may have a size of 16×16. When one coding unit is partitioned into four sub-coding units, the coding units may be partitioned in a quadtree form.

For example, when one coding unit is partitioned into two sub-coding units, the width dimension or the height dimension of one of the two sub-coding units may be half the width dimension or half the height dimension of the original coding unit, respectively. For example, when a coding unit of a size of 32×32 is vertically partitioned into two sub-coding units, each of the two sub-coding units may have a size of 16×32. For example, when a coding unit of a size of 32×32 is horizontally partitioned into two sub-coding units, each of the two sub-coding units may have a size of 32×16. When one coding unit is partitioned into two sub-coding units, the coding units may be partitioned in a binary tree form.

Referring to fig. 3, the size of an LCU having a minimum depth of 0 may be 64×64 pixels, and the size of an SCU having a maximum depth of 3 may be 8×8 pixels. Here, a CU having 64×64 pixels (i.e., LCU) may be represented by depth 0, a CU having 32×32 pixels may be represented by depth 1, a CU having 16×16 pixels may be represented by depth 2, and a CU having 8×8 pixels (i.e., SCU) may be represented by depth 3.

Further, information on whether a CU is to be partitioned may be represented by partition information of the CU. The partition information may be 1-bit information. Partition information may be included in all CUs except SCU. For example, a CU may not be partitioned when the value of partition information is 0, and a CU may be partitioned when the value of partition information is 1.

A CU that is no longer partitioned among a plurality of CUs partitioned from an LCU may be partitioned into at least one Prediction Unit (PU). This process may also be referred to as partitioning.

A PU may be a base unit for prediction. The PU may be encoded and decoded in any of a skip mode, an inter mode, and an intra mode. The PUs may be partitioned in various forms depending on the mode.

Further, the encoding unit may not be partitioned into a plurality of prediction units, and the encoding unit and the prediction unit may have the same size.

As shown in fig. 4, in skip mode, a CU may not be partitioned. In the skip mode, a 2N×2N mode 410 having the same size as a non-partitioned CU may be supported.

In inter mode, 8 partition forms may be supported in a CU. For example, in the inter mode, a 2n×2n mode 410, a 2n×n mode 415, an n×2n mode 420, an n×n mode 425, a 2n×nu mode 430, a 2n×nd mode 435, an nl×2n mode 440, and an nr×2n mode 445 may be supported. In intra mode, 2n×2n mode 410 and n×n mode 425 may be supported.

One coding unit may be partitioned into one or more prediction units. One prediction unit may be partitioned into one or more sub-prediction units.

For example, when one prediction unit is partitioned into four sub-prediction units, the width size and the height size of one of the four sub-prediction units may be half the width size and half the height size of the original prediction unit. For example, when a prediction unit of a size of 32×32 is partitioned into four sub-prediction units, each of the four sub-prediction units may have a size of 16×16. When one prediction unit is partitioned into four sub-prediction units, the prediction units may be partitioned in a quadtree form.

For example, when one prediction unit is partitioned into two sub prediction units, the width size or the height size of one of the two sub prediction units may be half the width size or half the height size of the original prediction unit. For example, when a prediction unit of a size of 32×32 is vertically partitioned into two sub-prediction units, each of the two sub-prediction units may have a size of 16×32. For example, when a prediction unit of a size of 32×32 is horizontally partitioned into two sub-prediction units, each of the two sub-prediction units may have a size of 32×16. When one prediction unit is partitioned into two sub-prediction units, the prediction units may be partitioned in a binary tree form.

A Transform Unit (TU) may be a basic unit for transformation, quantization, inverse transformation, and inverse quantization within a CU. The TU may have a square shape or a rectangular shape, etc. The TUs may be determined independently in terms of the size of the CU or the form of the CU, or both.

A CU that is no longer partitioned among CUs partitioned from an LCU may be partitioned into at least one TU. Here, the partition structure of the TUs may be a quadtree structure. For example, as shown in FIG. 5, one CU 510 may be partitioned one or more times according to a quadtree structure. The case where one CU is partitioned at least once may be referred to as recursive partitioning. By partitioning, one CU 510 may be formed of TUs having different sizes. Alternatively, a CU may be partitioned into at least one TU depending on the number of vertical lines partitioning the CU or the number of horizontal lines partitioning the CU, or both. A CU may be partitioned into TUs that are symmetric to each other, or may be partitioned into TUs that are asymmetric to each other. In order to partition a CU into TUs symmetric to each other, information of the size/shape of the TUs may be signaled and may be derived from the information of the size/shape of the CU.

Furthermore, the encoding unit may not be partitioned into the transform units, and the encoding unit and the transform unit may have the same size.

One coding unit may be partitioned into at least one transform unit, and one transform unit may be partitioned into at least one sub-transform unit.

For example, when one transform unit is partitioned into four sub-transform units, the width dimension and the height dimension of one of the four sub-transform units may be half the width dimension and half the height dimension of the original transform unit, respectively. For example, when a 32×32 sized transform unit is partitioned into four sub-transform units, each of the four sub-transform units may have a size of 16×16. When one transform unit is partitioned into four sub-transform units, the transform units may be partitioned in a quadtree form.

For example, when one transform unit is partitioned into two sub-transform units, the width dimension or the height dimension of one of the two sub-transform units may be half the width dimension or half the height dimension of the original transform unit, respectively. For example, when a transform unit of a size of 32×32 is vertically partitioned into two sub-transform units, each of the two sub-transform units may have a size of 16×32. For example, when a transform unit of a size of 32×32 is horizontally partitioned into two sub-transform units, each of the two sub-transform units may have a size of 32×16. When one transform unit is partitioned into two sub-transform units, the transform units may be partitioned in a binary tree form.

When the transformation is performed, the residual block may be transformed by using at least one of predetermined transformation methods. For example, the predetermined transform method may include Discrete Cosine Transform (DCT), discrete Sine Transform (DST), KLT, and the like. Which transform method is applied to transform the residual block may be determined by using at least one of: inter prediction mode information of the prediction unit, intra prediction mode information of the prediction unit, and size/shape of the transform block. Information indicating the transformation method may be signaled.

The intra prediction mode may be a non-directional mode or a directional mode. The non-directional mode may be a DC mode or a planar mode. The direction mode may be a prediction mode having a specific direction or angle, and the number of direction modes may be M equal to or greater than 1. The direction mode may be indicated as at least one of a mode number, a mode value, and a mode angle.

The number of intra prediction modes may be N equal to or greater than 1, including a non-directional mode and a directional mode.

The number of intra prediction modes may vary depending on the size of the block. For example, when the size of a block is 4×4 or 8×8, the number of intra prediction modes may be 67, when the size of a block is 16×16, the number of intra prediction modes may be 35, when the size of a block is 32×32, the number of intra prediction modes may be 19, and when the size of a block is 64×64, the number of intra prediction modes may be 7.

The number of intra prediction modes may be fixed to N regardless of the size of the block. For example, the number of intra prediction modes may be fixed to at least one of 35 or 67 regardless of the size of the block.

The number of intra prediction modes may vary depending on the type of color component. For example, the number of prediction modes may vary depending on whether the color component is a luminance signal or a chrominance signal.

Intra-coding and/or decoding may be performed by using sample values or coding parameters included in reconstructed neighboring blocks.

In order to encode/decode a current block according to intra prediction, it may be identified whether a sample included in a reconstructed neighboring block is available as a reference sample of an encoding/decoding target block. When there is a sample that cannot be used as a reference sample of the encoding/decoding target block, the sample value is copied and/or interpolated to a sample that cannot be used as a reference sample by using at least one sample among samples included in the reconstructed neighboring block, whereby a sample that cannot be used as a reference sample can be used as a reference sample of the encoding/decoding target block.

In intra prediction, a filter may be applied to at least one of the reference samples or the prediction samples based on at least one of an intra prediction mode and a size of an encoding/decoding target block. Here, the encoding/decoding target block may mean a current block, and may mean at least one of an encoding block, a prediction block, and a transform block. The type of filter applied to the reference samples or the prediction samples may vary depending on at least one of the intra prediction mode or the size/shape of the current block. The type of filter may vary depending on at least one of the number of filter taps, the filter coefficient values, or the filter strength.

In the non-directional planar mode among the intra prediction modes, when a prediction block of an encoding/decoding target block is generated, a sample value in the prediction block may be generated according to a sample point by using a weighted sum of an upper reference sample point of a current sample point, a left reference sample point of the current sample point, an upper right reference sample point of the current block, and a lower left reference sample point of the current block.

In the non-directional DC mode among the intra prediction modes, when a prediction block of an encoding/decoding target block is generated, the prediction block may be generated by a mean value of an upper reference sample of the current block and a left reference sample of the current block. Further, filtering may be performed on one or more upper rows and one or more left columns adjacent to the reference sample in the encoding/decoding block by using the reference sample value.

In case of a plurality of direction modes (angle modes) among the intra prediction modes, a prediction block may be generated by using an upper right reference sample and/or a lower left reference sample, and the plurality of direction modes may have different directions. To generate the predicted sample values, interpolation of real units may be performed.

In order to perform the intra prediction method, an intra prediction mode of a current prediction block may be predicted from intra prediction modes of neighboring prediction blocks adjacent to the current prediction block. In case of predicting an intra prediction mode of a current prediction block by using mode information predicted from neighboring intra prediction modes, when the current prediction block and the neighboring prediction block have the same intra prediction mode, information that the current prediction block and the neighboring prediction block have the same intra prediction mode may be transmitted by using predetermined flag information. When the intra prediction mode of the current prediction block is different from the intra prediction modes of neighboring prediction blocks, the intra prediction mode information of the encoding/decoding target block may be encoded by performing entropy encoding.

The quadrangle shown in fig. 7 may indicate an image (or screen). Furthermore, the arrows of fig. 7 may indicate the prediction direction. That is, an image may be encoded or decoded or both encoded and decoded according to a prediction direction. Each picture can be classified into an I picture (intra picture), a P picture (unidirectional prediction picture), a B picture (bi-prediction picture), and the like according to the coding type. Each picture may be encoded and decoded according to an encoding type of each picture.

When the image that is the encoding target is an I picture, the picture itself can be intra-encoded without inter prediction. When the image as the encoding target is a P picture, the image may be encoded by inter prediction or motion compensation using a reference picture only in the forward direction. When the image as the encoding target is a B picture, the image can be encoded by inter prediction or motion compensation using reference pictures in both the forward and reverse directions. Alternatively, the image may be encoded by inter prediction or motion compensation using a reference picture in one of the forward and reverse directions. Here, when the inter prediction mode is used, the encoder may perform inter prediction or motion compensation, and the decoder may perform motion compensation in response to the encoder. The images of the P picture and the B picture, which are encoded or decoded using the reference picture or are encoded and decoded, may be regarded as images for inter prediction.

Hereinafter, the inter prediction according to the embodiment will be described in detail.

Inter prediction or motion compensation may be performed by using both reference pictures and motion information. In addition, inter prediction may use the skip mode described above.

The reference picture may be at least one of a previous picture and a subsequent picture of the current picture. Here, the inter prediction may predict a block of the current picture from the reference picture. Here, the reference picture may mean an image used in predicting a block. Here, the region within the reference picture may be indicated by using a reference picture index (refIdx) indicating the reference picture, a motion vector, or the like.

Inter prediction may select a reference picture and a reference block within the reference picture that is associated with the current block. The prediction block of the current block may be generated by using the selected reference block. The current block may be a block as a current encoding target or a current decoding target among blocks of the current picture.

The motion information may be derived from the processing of inter prediction by the encoding apparatus 100 and decoding apparatus 200. Furthermore, the derived motion information may be used when performing inter prediction. Here, the encoding apparatus 100 and the decoding apparatus 200 may improve encoding efficiency or decoding efficiency or both by using motion information of reconstructed neighboring blocks or motion information of co-located blocks (col blocks) or both. The col block may be a block within a previously reconstructed co-located picture (col picture) that is related to the spatial position of the encoding/decoding target block. The reconstructed neighboring block may be a block within the current picture, as well as a block previously reconstructed by encoding or decoding or both. Further, the reconstructed block may be a block adjacent to the encoding/decoding target block, or a block located at an outer corner of the encoding/decoding target block, or both. Here, the block located at the outer corner of the encoding/decoding target block may be a block vertically adjacent to an adjacent block horizontally adjacent to the encoding/decoding target block. Alternatively, the block located at the outer corner of the encoding/decoding target block may be a block horizontally adjacent to an adjacent block vertically adjacent to the encoding/decoding target block.

The encoding apparatus 100 and the decoding apparatus 200 may determine blocks existing at positions spatially related to the encoding/decoding target block within the col picture, respectively, and may determine the predefined relative positions based on the determined blocks. The predefined relative position may be an internal position or an external position of a block existing at a position spatially related to the encoding/decoding target block or both the internal position and the external position. Furthermore, the encoding device 100 and the decoding device 200 may derive col blocks, respectively, based on the determined predefined relative positions. Here, the col picture may be one picture of at least one reference picture included in the reference picture list.

The method of deriving motion information may vary according to the prediction mode of the encoding/decoding target block. For example, the prediction modes applied to the inter prediction may include Advanced Motion Vector Prediction (AMVP), merge mode, and the like. Here, the merge mode may be referred to as a motion merge mode.

For example, when AMVP is applied as a prediction mode, the encoding apparatus 100 and the decoding apparatus 200 may generate a motion vector candidate list by using a motion vector of a reconstructed neighboring block or a motion vector of a col block or both, respectively. Either the motion vector of the reconstructed neighboring block or the motion vector of the col block or both may be used as motion vector candidates. Here, the motion vector of the col block may be referred to as a temporal motion vector candidate, and the motion vector of the reconstructed neighboring block may be referred to as a spatial motion vector candidate.

The encoding apparatus 100 may generate a bitstream, which may include the motion vector candidate index. That is, the encoding apparatus 100 may generate a bitstream by entropy encoding the motion vector candidate index. The motion vector candidate index may indicate an optimal motion vector candidate selected from among motion vector candidates included in the motion vector candidate list. The motion vector candidate index may be transmitted from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream.

The decoding apparatus 200 may entropy-decode the motion vector candidate index from the bitstream, and may select a motion vector candidate of the decoding target block among the motion vector candidates included in the motion vector candidate list by using the entropy-decoded motion vector candidate index.

The encoding apparatus 100 may calculate a Motion Vector Difference (MVD) between a motion vector of a decoding target block and a motion vector candidate, and may entropy-encode the MVD. The bitstream may include entropy encoded MVDs. The MVD may be transmitted from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream. Here, the decoding apparatus 200 may entropy-decode MVDs received from the bitstream. The decoding apparatus 200 may derive a motion vector of the decoding target block from the sum of the decoded MVD and the motion vector candidates.

The bitstream may include a reference picture index indicating a reference picture, etc., and the reference picture index may be entropy encoded and transmitted from the encoding apparatus 100 to the decoding apparatus 200 through the bitstream. The decoding apparatus 200 may predict a motion vector of the decoding target block by using motion information of neighboring blocks and may derive the motion vector of the decoding target block by using the predicted motion vector and the motion vector difference. The decoding apparatus 200 may generate a prediction block of the decoding target block based on the derived motion vector and the reference picture index information.

As another method of deriving motion information, a merge mode is used. The merge mode may mean a merging of motions of a plurality of blocks. A merge mode may mean that motion information of one block is applied to another block. When the merge mode is applied, the encoding apparatus 100 and the decoding apparatus 200 may generate a merge candidate list by using motion information of a reconstructed neighboring block or motion information of a col block or both, respectively. The motion information may include at least one of: 1) motion vectors, 2) reference picture indices, and 3) inter prediction indicators. The prediction indicator may indicate unidirectional (L0 prediction, L1 prediction) or bidirectional.

Here, the merge mode may be applied to each CU or each PU. When the merge mode is performed at each CU or each PU, the encoding apparatus 100 may generate a bitstream by entropy decoding predefined information and may transmit the bitstream to the decoding apparatus 200. The bitstream may comprise said predefined information. The predefined information may include: 1) A merge flag as information indicating whether a merge mode is performed for each block partition, 2) a merge index as information indicating which block is merged among neighboring blocks adjacent to the encoding target block. For example, neighboring blocks adjacent to the encoding target block may include a left neighboring block of the encoding target block, an upper neighboring block of the encoding target block, a temporal neighboring block of the encoding target block, and the like.

The merge candidate list may indicate a list storing motion information. Further, a merge candidate list may be generated before the merge mode is performed. The motion information stored in the merge candidate list may be at least one of the following motion information: the motion information of a neighboring block adjacent to the encoding/decoding target block, the motion information of a co-located block in the reference picture related to the encoding/decoding target block, the motion information newly generated by the pre-combining of the motion information existing in the motion candidate list, and the zero merge candidate. Here, the motion information of neighboring blocks adjacent to the encoding/decoding target block may be referred to as spatial merging candidates. The motion information of the co-located block in the reference picture related to the encoding/decoding target block may be referred to as a temporal merging candidate.

The skip mode may be a mode in which mode information of neighboring blocks themselves is applied to the encoding/decoding target block. The skip mode may be one of modes for inter prediction. When the skip mode is used, the encoding apparatus 100 may entropy-encode information about which block motion information is used as the motion information of the encoding target block, and may transmit the information to the decoding apparatus 200 through a bitstream. The encoding apparatus 100 may not transmit other information (e.g., syntax element information) to the decoding apparatus 200. The syntax element information may include at least one of motion vector difference information, a coded block flag, and a transform coefficient level.

The residual signal generated after intra prediction or inter prediction may be transformed into the frequency domain through a transform process as part of a quantization process. Here, the first transformation may use DCT type 2 (DCT-II) as well as various DCT, DST kernels. These transform kernels may perform a separable transform on the residual signal for performing a 1D transform in the horizontal and/or vertical directions, or may perform a 2D inseparable transform on the residual signal.

For example, in the case of a 1D transform, DCT-II, DCT-V, DCT-VIII, DST-I, and DST-VII as shown in the following tables may be used for the DCT and DST types used in the transform. For example, as shown in tables 1 and 2, the DCT or DST type used in the transformation by synthesizing the transformation set can be derived.

TABLE 1

Transform set	Transformation
		0	DST_VII、DCT-VIII
1	DST-VII、DST-I
		2	DST-VII、DCT-V

TABLE 2

Transform set	Transformation
		0	DST_VII、DCT-VIII、DST-I
1	DST-VII、DST-I、DCT-VIII
		2	DST-VII、DCT-V、DST-I

For example, as shown in fig. 8, different transform sets are defined for the horizontal direction and the vertical direction according to the intra prediction mode. Next, the encoder/decoder may perform transformation and/or inverse transformation by transforming using the intra prediction mode of the current encoding/decoding target block and the related transformation set. In this case, entropy encoding/decoding is not performed on the transform set, and the encoder/decoder may define the transform set according to the same rule. In this case, entropy encoding/decoding indicating which transform is used among the transforms of the transform set may be performed. For example, when the size of a block is equal to or smaller than 64×64, three transform sets are synthesized according to the intra prediction mode as shown in table 2, and three transforms are used for each horizontal direction transform and vertical direction transform to combine and perform a total of nine transform methods. Next, the residual signal is encoded/decoded by using an optimal transform method, whereby encoding efficiency can be improved. Here, in order to entropy encode/decode information on which transform method is used among three transforms in one transform set, truncated unary binarization may be used. Here, in order to perform at least one of the vertical transform and the horizontal transform, entropy encoding/decoding may be performed on information indicating which one of the transforms of the transform set is used.

After completing the above-described first transform, as shown in fig. 9, the encoder may perform a second transform for the transform coefficients to increase the energy concentration. The secondary transform may perform a separable transform for performing a 1D transform in a horizontal and/or vertical direction, or may perform a 2D non-separable transform. The transformation information used may be transmitted or may be derived by the encoder/decoder from the current encoding information and the neighboring encoding information. For example, as a 1D transform, a set of transforms for a secondary transform may be defined. Entropy encoding/decoding is not performed on the transform set, and the encoder/decoder may define the transform set according to the same rule. In this case, information indicating which transform among the transforms of the transform set is used may be transmitted, and the information may be applied to at least one residual signal through intra prediction or inter prediction.

At least one of the number or type of transform candidates is different for each set of transforms. At least one of the number or type of transform candidates may be determined differently based on at least one of: the location, size, partition form, and prediction mode (intra/inter mode) or direction/non-direction of intra prediction mode of blocks (CU, PU, TU, etc.).

The decoder may perform the secondary inverse transform depending on whether the secondary inverse transform is performed, and may perform the primary inverse transform depending on whether the primary inverse transform is performed from the result of the secondary inverse transform.

The above-described primary transform and secondary transform may be applied to at least one signal component among luminance/chrominance components, or may be applied according to the size/shape of an arbitrary encoding block. Entropy encoding/decoding may be performed on indexes indicating whether the first transform/secondary transform is used or not and both the used first transform/secondary transform in any encoding block. Alternatively, the index may be derived by default by the encoder/decoder from at least one piece of current/neighboring coding information.

The residual signal generated after intra prediction or inter prediction is subjected to quantization processing after being subjected to primary transform and/or secondary transform, and the quantized transform coefficient is subjected to entropy encoding processing. Here, as shown in fig. 10, the quantized transform coefficients may be scanned in a diagonal direction, a vertical direction, and a horizontal direction based on at least one of an intra prediction mode or a size/shape of a minimum block.

Further, the quantized transform coefficients, on which entropy decoding is performed, may be arranged in a block form by being inversely scanned, and at least one of inverse quantization or inverse transformation may be performed on the relevant blocks. Here, as a method of the inverse scan, at least one of the diagonal direction scan, the horizontal direction scan, and the vertical direction scan may be performed.

For example, when the size of the current encoding block is 8×8, first transform, second transform, and quantization may be performed on the residual signal for the 8×8 block, and next, scan and entropy encoding may be performed on the quantized transform coefficients for each of the four 4×4 sub-blocks according to at least one of the three scan order methods shown in fig. 10. Further, inverse scanning may be performed on the quantized transform coefficients by performing entropy decoding. The quantized transform coefficients on which the inverse scan is performed become transform coefficients after being inverse quantized, and at least one of a secondary inverse transform or a primary inverse transform is performed, whereby a reconstructed residual signal can be generated.

In the video encoding process, one block may be partitioned as shown in fig. 11, and an indicator corresponding to partition information may be signaled. Here, the partition information may be at least one of: partition flag (split_flag), quadtree partition flag (qb_flag), quadtree partition flag (quadtree_flag), binary tree partition flag (binaryre_flag), and binary tree partition type flag (btype_flag). Here, split_flag is a flag indicating whether a block is partitioned or not, qb_flag is a flag indicating whether a block is partitioned in a quadtree form or a binary tree form, quadtree_flag is a flag indicating whether a block is partitioned in a quadtree form or not, binaryre_flag is a flag indicating whether a block is partitioned in a binary tree form or not, btype_flag is a flag indicating whether a block is vertically partitioned or horizontally partitioned in the case of partition in a binary tree form.

When the partition flag is 1, it may indicate that the partition is executed, and when the partition flag is 0, it may indicate that the partition is not executed. In the case of a quadtree/binary tree flag, 0 may indicate a quadtree partition and 1 may indicate a binary tree partition. Alternatively, 0 may indicate a binary tree partition and 1 may indicate a quadtree partition. In the case of a binary tree partition type flag, 0 may indicate a horizontal direction partition and 1 may indicate a vertical direction partition. Alternatively, 0 may indicate a vertical direction zone and 1 may indicate a horizontal direction zone.

For example, the partition information of fig. 11 may be derived by signaling at least one of quadtree_ flag, binarytree _flag and btype_flag as shown in table 3.

TABLE 3

For example, the partition information of fig. 11 may be derived by signaling at least one of split_flag, qb_flag, and btype_flag as shown in table 4.

TABLE 4

The partitioning method may be performed only in a quadtree form or only in a binary tree form according to the size/shape of the block. In this case, the split_flag may mean a flag indicating whether the partitioning is performed in the quadtree form or the binary tree form. The size/shape of the block may be derived from the depth information of the block, and the depth information may be signaled.

When the size of the block is in a predetermined range, the partitioning may be performed only in a quadtree form. Here, the predetermined range may be defined as at least one of a size of a maximum block or a size of a minimum block that can be partitioned only in a quadtree form. Information indicating the size of the maximum block/minimum block of partitions allowed in the form of a quadtree may be signaled through a bitstream, and may be signaled in units of at least one of a sequence, a picture parameter, or a slice (segment). Alternatively, the size of the maximum block/minimum block may be a fixed size preset in the encoder/decoder. For example, when the size of a block ranges from 256×256 to 64×64, the partitioning may be performed only in a quadtree form. In this case, the split_flag may be a flag indicating whether or not the partitioning is performed in the quadtree form.

When the size of the block is in a predetermined range, the partitioning may be performed only in a binary tree form. Here, the predetermined range may be defined as at least one of a size of a maximum block or a size of a minimum block that can be partitioned only in a binary tree form. Information indicating the size of the largest/smallest block of partitions that are allowed to be in the form of a binary tree may be signaled through a bitstream, and may be signaled in units of at least one of a sequence, a picture parameter, or a stripe (segment). Alternatively, the size of the maximum block/minimum block may be a fixed size preset in the encoder/decoder. For example, when the size of a block ranges from 16×16 to 8×8, the partitioning may be performed only in a binary tree form. In this case, the split_flag may be a flag indicating whether or not the partitioning is performed in a binary tree form.

After partitioning a block in a binary tree form, partitioning may be performed only in a binary tree form when the partitioned block is further partitioned.

At least one indicator may not be signaled when the width or length dimensions of the partitioned blocks cannot be further partitioned.

In addition to the quadtree-based binary tree partitioning, the quadtree-based partitioning may be performed after the binary tree partitioning.

As shown in fig. 12, intra prediction may include deriving an intra prediction mode (S1210), constructing a reference sample (S1220), and/or performing intra prediction (S1230).

In the step of deriving the intra prediction mode (S1210), the intra prediction mode of the current block may be decoded (e.g., entropy decoded) from the bitstream using the intra prediction modes of the neighboring blocks, and/or the intra prediction mode of the current block may be derived using the encoding parameters of the neighboring blocks. Alternatively, in the step of deriving the intra prediction mode (S1210), the intra prediction mode of the current block may be derived using the intra prediction mode of the neighboring block, a combination of one or more intra prediction modes of the neighboring block, and/or the intra prediction mode derived by the MPM.

In the step of constructing the reference sample (S1220), the reference sample may be constructed by performing reference sample selection and/or reference sample filtering.

In the step of performing intra prediction (S1230), intra prediction may be performed on the current block using non-directional prediction, prediction based on location information, and/or prediction based on luminance/chrominance signals. In the step of performing intra prediction (S1230), filtering may be additionally performed on the prediction samples. If direction prediction is performed, different direction predictions may be performed according to one or more sample units. For example, the one or more sample units may be a single sample, a group of samples, a row, and/or a sub-block.

Hereinafter, the step of deriving the intra prediction mode (S1210) will be described in more detail.

As described above, in order to derive an intra prediction mode of a current block, at least one of the following methods may be used: methods of using intra prediction modes of one or more neighboring blocks, methods of decoding intra prediction modes of a current block from a bitstream, and methods of using coding parameters of neighboring blocks. The neighboring blocks may be one or more blocks reconstructed before encoding/decoding the current block.

If the neighboring block is located outside the boundary of at least one predetermined unit, such as a picture, a slice, a parallel block, and a Coding Tree Unit (CTU), or PCM mode or inter prediction has been applied to the neighboring block, it may be determined that the neighboring block is not available. The intra prediction mode corresponding to the unavailable neighboring block may be replaced by a DC mode, a planar mode, or a predetermined intra prediction mode.

The size of the current block may be w×h, where W and H are positive integers and may be equal or different. W and/or H may be, for example, at least one of 2, 4, 8, 16, 32, 64, 128, 256, and 512.

In fig. 13, a to k marked on the neighboring block may represent an intra prediction mode or a mode number of the neighboring block. The location of the neighboring blocks used to derive the intra prediction mode of the current block may be a predefined fixed location. Alternatively, information about the locations of neighboring blocks may be derived by encoding/decoding. In the present disclosure, encoding/decoding may be used to include entropy encoding and entropy decoding.

In case of using the intra prediction mode of the neighboring block, the specific mode of the neighboring block may be derived as the intra prediction mode of the current block. For example, the intra prediction mode i of a neighboring block to which a left-side sample (-1, 0) adjacent to the sample (0, 0) of the current block belongs may be derived as the intra prediction mode of the current block. Alternatively, the intra prediction mode f of the neighboring block to which the upper sample (0, -1) adjacent to the sample (0, 0) of the current block belongs may be derived as the intra prediction mode of the current block. Alternatively, the intra prediction mode b of the neighboring block to which the leftmost upsampling point (-1, -1) neighboring the upsampling point (0, 0) of the current block belongs may be derived as the intra prediction mode of the current block. Alternatively, the intra prediction mode g of the neighboring block to which the upper sample (W-1, -1) adjacent to the sample (W-1, 0) of the current block belongs may be derived as the intra prediction mode of the current block. Alternatively, the intra prediction mode k of the neighboring block to which the rightmost upsampling point (W, -1) neighboring the upsampling point (W-1, 0) of the current block belongs may be derived as the intra prediction mode of the current block. Alternatively, the intra prediction mode j of the neighboring block to which the left-side sample (1, h-1) adjacent to the sample (0, h-1) of the current block belongs may be derived as the intra prediction mode of the current block. Alternatively, the intra prediction mode l of the neighboring block to which the leftmost lower sample (-1, h) adjacent to the sample (0, h-1) of the current block belongs may be derived as the intra prediction mode of the current block. Alternatively, the intra prediction mode of a neighboring block at a predetermined position among neighboring blocks may be derived as the intra prediction mode of the current block. For example, the predetermined position may be encoded/decoded from the bitstream, or may be derived based on encoding parameters. For example, the predetermined position may be a block having an intra prediction mode e.

Alternatively, one or more of the neighboring blocks of the current block may be selected. The selection may be made based on information explicitly signaled by the bitstream. Alternatively, the selection may be made according to a pre-set criterion between the encoder and the decoder. The intra prediction mode of the current block may be derived from the intra prediction modes of the selected one or more neighboring blocks. For example, the intra prediction mode of the current block may be derived using statistics of intra prediction modes of selected neighboring blocks. For example, the statistics may include a minimum, a maximum, a mean, a weighted value, a most frequent value, and/or a median.

For example, a mode having a smaller or higher mode number between intra prediction modes i and f of neighboring blocks to which a left side sample adjacent to a sample (0, 0) of the current block and an upper sample belong may be derived as an intra prediction mode of the current block. For example, if the intra prediction modes of the selected neighboring blocks are b, f, g, i and j, the mode having the smallest mode number among the mode numbers of the intra prediction modes may be derived as the intra prediction mode of the current block. For example, if the intra prediction modes of the selected neighboring block are i, b, and f, a mode having a median value of mode numbers of the intra prediction modes may be derived as the intra prediction mode of the current block. For example, the most frequent intra prediction mode among intra prediction modes of neighboring blocks adjacent to the current block may be derived as the intra prediction mode of the current block.

Alternatively, the intra prediction mode of the current block may be derived by combining intra prediction modes of one or more neighboring blocks. The intra prediction mode may be represented as at least one of a mode number, a mode value, and a mode angle. For example, a mean of one or more intra prediction modes of neighboring blocks may be derived as an intra prediction mode of the current block. The mean of two intra prediction modes may refer to at least one of: an intermediate number between the two pattern numbers, a median of the two pattern values, and an intermediate angle between the two pattern angles.

For example, a mode corresponding to the average of mode values of intra prediction modes i and f of neighboring blocks to which a left side sample and an upper side sample adjacent to the sample (0, 0) of the current block belong may be derived as the intra prediction mode of the current block. For example, the intra prediction mode pred_mode of the current block may be derived by at least one of the methods (1), (2), and (3) described in [ equation 1 ].

[ equation 1]

Pred_mode＝(i+f)>>1(1)

Pred_mode＝(i+f+1)>>1(2)

Pred_mode＝(i+f)/2(3)

Alternatively, if the intra prediction mode i of the neighboring block is a non-directional mode, the intra prediction mode of the current block may be derived as the intra prediction mode i. Alternatively, if the intra prediction mode f of the neighboring block is a directional mode, the intra prediction mode of the current block may be derived as the intra prediction mode f.

Alternatively, the intra prediction mode of the current block may be derived as a mode corresponding to a mean value of at least one of the mode values of the intra prediction modes b, f, g, i and j of the neighboring blocks. For example, the intra prediction mode pred_mode of the current block may be derived by at least one of the methods (1), (2), (3), and (4) described in [ equation 2 ].

[ equation 2]

Pred_mode＝(f+g+i+j+2)>>2(1)

Pred_mode＝(b+f+g+i+j)/5(2)

Pred_mode＝(i+f+k+l+2)>>2(3)

Pred_mode＝(b+f+k+i+l)/5(4)

Alternatively, a mode corresponding to the mean of available intra prediction modes of neighboring blocks may be derived as the intra prediction mode of the current block. For example, if a left neighboring block of the current block is located outside the boundary of a picture, a parallel block, a slice, and/or a CTU, or corresponds to at least one of a PCM mode or an intra prediction mode and is thus unavailable, a mode corresponding to statistics of intra prediction modes (e.g., f and g) of an upper neighboring block may be derived as the intra prediction mode of the current block.

For example, the weighted mean or weighted sum may be used as a statistic of intra prediction modes of neighboring blocks. Here, the weights may be assigned based on directions of intra prediction modes of neighboring blocks. For example, the mode assigned a relatively large weight may be predefined or signaled. For example, the mode assigned with a relatively large weight may be at least one of a vertical direction mode, a horizontal direction mode, and a non-direction mode. These modes may be assigned the same weight or different weights. For example, the weighted sum of intra prediction modes i and f may be derived as an intra prediction mode pred_mode of the current block by [ equation 3] below. In the following [ equation 3], the pattern f may be a pattern (e.g., a vertical direction pattern) assigned with a relatively large weight.

[ equation 3]

Pred_mode＝(i+3*f+2)>>2

Alternatively, the weights to be used for the weighted sum may be determined based on the size of the neighboring blocks. For example, if the size of an upper block adjacent to the current block is greater than the size of a left block adjacent to the current block, a greater weight may be assigned to the intra prediction mode of the upper adjacent block. Alternatively, larger weights may be assigned to intra prediction modes of smaller neighboring blocks.

Alternatively, if one or more intra prediction modes of neighboring blocks are non-directional modes, the non-directional modes may be derived as intra prediction modes of the current block. Alternatively, the intra prediction mode of the current block may be derived using intra prediction modes of neighboring blocks other than the non-directional mode. If all intra prediction modes of neighboring blocks are non-directional modes, the intra prediction mode of the current block may be derived as at least one of a DC mode or a planar mode.

Alternatively, the intra prediction mode of the current block may be derived using the Most Probable Mode (MPM) based on the intra prediction modes of neighboring blocks. If the MPM is used, one or more pieces of information regarding the intra prediction mode of the current block may be encoded/decoded.

If MPM is used, the MPM list may be configured. The MPM list may include intra-prediction modes derived based on intra-prediction modes of neighboring blocks. The MPM list may include N candidate patterns. N is a positive integer and may vary depending on the size and/or shape of the current block. Alternatively, the information about N may be signaled by a bitstream.

For example, an intra prediction mode of the current block, which is derived using one or more intra prediction modes of neighboring blocks, may be a candidate mode included in the MPM list.

In the example shown in fig. 13, intra prediction modes of neighboring blocks at the same positions of (-1, h-1), (W-1, -1), (W-1), (-1, h), and (-1, -1) adjacent to the current block may be used, and for example, MPM lists may be made in the order of j, g, plane, DC, l, k, and b. The repetition pattern may be included once in the MPM list. If the MPM list is not filled due to the presence of the repeating pattern, additional candidate patterns may be included in the list based on the patterns included in the list. For example, a pattern corresponding to +n or-N (N is a positive integer, e.g., 1) of the patterns included in the list may be added to the list. Alternatively, at least one of a horizontal mode, a vertical mode, a 45 degree mode, a 135 degree mode, and a 225 degree mode, which are not included in the list, may be added to the list.

An indicator (e.g., prev _ intra _ luma _ pred _ flag) indicating whether the same mode as the intra prediction mode of the current block exists in the derived MPM list may be encoded into or decoded from the bitstream.

If the indicator indicates that there is the same mode as the intra prediction mode of the current block in the MPM list, index information (e.g., mpm_idx) indicating which mode among modes included in the MPM list is encoded into or decoded from the bitstream. The intra prediction mode of the current block may be derived based on the decoded index information.

If the indicator indicates that the same mode as the intra prediction mode of the current block does not exist in the MPM list, information regarding the intra prediction mode of the current block may be encoded into or decoded from the bitstream. The intra prediction mode of the current block may be derived based on the decoded information on the intra prediction mode of the current block. Here, the intra prediction modes not included in the MPM list may be arranged in at least one of an ascending order or a descending order. Alternatively, one or more of the intra prediction modes not included in the MPM list may be grouped into one or more groups. For example, modes corresponding to +n or-N (N is a positive integer, e.g., 1, 2, or 3) of intra prediction modes included in the MPM list may be grouped into a group. Here, the group may include a predetermined number (e.g., 8 or 16) of intra prediction modes, and the modes included in the group may not be included in the MPM list.

Alternatively, the predetermined candidates in the derived MPM list may be derived as the intra prediction mode of the current block. For example, a mode corresponding to list 0 (i.e., a first mode in the MPM list) may be derived as an intra prediction mode of the current block. Alternatively, an index corresponding to a predetermined mode in the list may be encoded/decoded, and the corresponding mode may be derived as an intra prediction mode of the current block.

Regarding the configuration of the MPM list, one MPM list may be made for a block of a predetermined size. If the predetermined-sized block is divided into a plurality of sub-blocks, each of the plurality of sub-blocks may use the MPM list.

For example, if the current block corresponds to the predetermined-sized block, an MPM list may be made for the current block. If the current block is divided into one or more sub-blocks, an intra prediction mode may be derived for each sub-block using the MPM list. For example, if the size of the current block is 8×8 and is divided into 4 4×4 sub-blocks, an MPM list may be made for the current block, and the list may be used for each sub-block.

Regarding the configuration of the MPM list, the MPM list may be made for each sub-block into which a block of a predetermined size is divided.

For example, if the current block corresponds to the predetermined-sized block, an MPM list may be made for each sub-block of the current block using intra prediction modes of neighboring blocks of the current block. For example, if the size of the current block is 8×8 and there are 4 4×4 sub-blocks, an MPM list may be made for each of the four sub-blocks using intra prediction modes of neighboring blocks of the current block. Thus, the MPM list may be made simultaneously for the four sub-blocks.

Alternatively, the intra prediction mode of the current block may be derived using at least one of the intra prediction mode of the current block and the intra prediction modes of neighboring blocks derived by the MPM.

For example, if the intra prediction mode of the current block, which is derived by the MPM, is pred_mpm, the intra prediction mode of the current block may be derived by changing pred_mpm to a specific mode using one or more intra prediction modes of neighboring blocks.

For example, pred_mpm may be increased or decreased by N by comparing the pred_mpm to intra prediction modes of neighboring blocks in size. Here, N may be a predetermined integer such as +1, +2, +3, 0, -1, -2, or-3. For example, pred_mpm may be increased if pred_mpm is less than the intra-prediction mode of the neighboring block and/or the statistics of intra-prediction modes of one or more neighboring blocks. Alternatively, pred_mpm may be reduced if pred_mpm is greater than the intra prediction modes of neighboring blocks. Alternatively, the intra prediction mode of the current block may be derived based on pred_mpm and/or a value compared to pred_mpm.

In the example shown in fig. 13, if pred_mpm is smaller than the mode value of f, pred_mpm+1 may be derived as the intra prediction mode of the current block. Alternatively, if pred_mpm is less than the mode value of g, pred_mpm+1 may be derived as the intra prediction mode of the current block. Alternatively, if pred_mpm is smaller than the mode value of f, pred_mpm+2 may be derived as the intra prediction mode of the current block. Alternatively, if pred_mpm is greater than the mode value of f, pred_mpm-1 may be derived as the intra prediction mode of the current block. Alternatively, if pred_mpm is less than the mode value of i, pred_mpm+1 may be derived as the intra prediction mode of the current block. Alternatively, if pred_mpm is smaller than the average of the mode values of f and i, pred_mpm+1 may be derived as the intra prediction mode of the current block. Alternatively, if pred_mpm is less than the average of the mode values of f and i, the difference between pred_mpm and the average may be increased by 1/2. For example, pred_mpm+ { ((f+i+1) > > 1-pred_mpm+1) > >1} may be derived as the intra prediction mode of the current block.

Alternatively, if one of the modes of the pred_mpm and the neighboring block is a non-directional mode and the other is a directional mode, the non-directional mode may be derived as an intra prediction mode of the current block, or the directional mode may be derived as an intra prediction mode of the current block.

As described previously, the intra prediction mode of the current block may be derived through encoding/decoding. Here, the intra prediction modes of neighboring blocks may not be used. For example, the intra prediction mode of the current block may be derived by entropy encoding/decoding the bitstream.

For example, if the current block is divided into lower blocks or sub-blocks, the intra prediction mode of each sub-block may be derived using at least one of the methods for deriving the intra prediction mode of the current block described previously.

The size of the current block and the size of the sub-block may be mxn. M and N may be the same positive integer or different positive integers. For example, the current block or sub-block may be at least one of CTU, CU, SU (signaling unit), QTMax, QTMin, BTMax, BTMin, 4×4, 8×8, 16×16, 32×32, 64×64, 128×128, 256×256, 4×8, 8×16, 16×8, 32×64, 32×8, and 4×32 in size. Here, QTMax and QTMin may represent maximum and minimum sizes allowed to be divided into a quadtree, respectively, and BTMax and BTMin may represent maximum and minimum sizes allowed to be divided into a binary tree, respectively. Hereinafter, the size of the sub-block may mean a division structure of the sub-block.

The sub-block size may vary depending on the size of the current block. For example, 1/N of the horizontal size and the vertical size of the current block may be a sub-block size. N may be a positive integer and may be at least one of 2, 4, 8, 16, 32, and 64. For example, if the size of the current block is 32×32 and N in 1/N of the horizontal and vertical sizes of the current block is 4, the sub-block size may be 8×8.

Alternatively, the sub-block size may be a predetermined fixed size regardless of the size of the current block. For example, the sub-block size may be the minimum size regardless of the size of the current block, and may be, for example, 4×4.

Alternatively, the sub-block size may be determined based on the partition structure of neighboring blocks of the current block. For example, if neighboring blocks are divided, the sub-block size may be determined by dividing the current block.

The sub-block size may be determined based on intra prediction modes of neighboring blocks of the current block. For example, the sub-block size may be determined by block division into sub-blocks based on intra prediction modes of neighboring blocks becoming different boundaries.

The sub-block size may be determined based on coding parameters of neighboring blocks. For example, the sub-block size may be determined by block partitioning into sub-blocks based on whether neighboring blocks are intra-coded or inter-coded blocks.

At least one of the current block size, the sub-block size, and N according to which the current block is divided may be fixed to a predetermined value.

For example, in case that the predetermined fixed size of the current block is 16×16, if the size of the current block is 16×16, the current block may be divided into sub-blocks and an intra prediction mode of each sub-block may be derived.

For example, in case that the predetermined fixed size of the current block is CTU and N is 4, if the size of the current block is CTU, an intra prediction mode may be derived based on the sub-blocks, each sub-block being obtained by dividing latitude and longitude of the CTU by 4.

The one or more sub-blocks may be further divided into smaller blocks. For example, if the current block is 32×32 in size and the sub-block is 16×16 in size, each of the one or more sub-blocks may be divided into smaller sub-blocks each having a size of 8×8, 4×4, 16×8, 4×16, etc.

At least one of the current block size, the sub-block size, and N according to which the current block is divided may be encoded/decoded.

The partition structure for the sub-block of the current block may be encoded/decoded. The sub-blocks into which the current block is divided may vary in size and/or shape. Furthermore, an intra prediction mode may be derived for each sub-block.

An indicator (e.g., a flag) indicating that the intra prediction mode of the current block is derived using the intra prediction modes of neighboring blocks may be encoded/decoded. For example, the indicator may be ndip_flag (neighbor mode dependent intra prediction). The indicator may be encoded/decoded for at least one of the current block or each sub-block. The indicator may be encoded/decoded only when the current block size or sub-block size corresponds to a predetermined size or a predetermined size range. The predetermined size may be, for example, 64×64 or BTMax. As previously described, the current block may be divided into a plurality of sub-blocks. The partition structure of the sub-blocks may be predefined or encoded/decoded.

If ndip_flag is 1 for the current block, intra prediction modes of neighboring blocks may be used to derive intra prediction modes of the current block or of each sub-block of the current block. In this case, at least one of prev_intra_luma_pred_flag, mpm_idx, rem_intra_luma_pred_mode, intra_chroma_pred_mode, split_flag, qb_ flag, quadtree _ flag, binarytree _flag, and btype_flag for the current block and/or sub-block may not be encoded/decoded.

If ndip_flag is 1 for the current block, the intra prediction mode of the current block may be encoded, and then the intra prediction mode of each sub-block may be derived using the decoded intra prediction mode and the intra prediction modes of neighboring blocks. Here, at least one of the prev_intra_luma_pred_flag, mpm_idx, rem_intra_luma_pred_mode, intra_chroma_pred_mode, split_flag, qb_ flag, quadtree _ flag, binarytree _flag, and btype_flag for the sub-block may not be encoded/decoded.

If ndip_flag is 0 for the current block, information related to at least one of intra prediction mode of the current block or sub-block and partition information of the sub-block may be encoded/decoded.

Among the sub-blocks of the current block, the intra prediction mode of the first sub-block may be derived in a different manner from other sub-blocks. The first sub-block may be one of a plurality of sub-blocks of the current block. For example, the first sub-block may be a first sub-block in a Z-scan order.

The intra prediction mode of the first sub-block may refer to an initial mode. For example, if the intra prediction mode of each sub-block is derived as the average of the intra prediction modes of the blocks to the left and above the sub-block, the initial mode may be derived in a different method. The different method for deriving the initial mode may be at least one of the methods for deriving an intra prediction mode according to the present invention.

For example, an nth (e.g., first) pattern listed in the MPM list may be derived as the initial pattern. Alternatively, the most frequent one of the intra prediction modes of one or more neighboring blocks of the current block may be derived as the initial mode. Alternatively, the intra prediction mode encoded/decoded for the current block may be derived as the initial mode. Alternatively, the intra prediction mode encoded/decoded for the first sub-block may be derived as the initial mode.

Regarding the derivation of intra prediction modes for sub-blocks in a current block, intra prediction modes for one or more sub-blocks may be derived in any order. The arbitrary order may be a scanning order, and the scanning may correspond to at least one of the following scanning: raster scan, top right scan, vertical scan, horizontal scan, diagonal scan, and zig-zag scan. The number of sub-blocks for deriving the intra prediction mode in scan order may be 1 or more. The arbitrary order may be adaptively determined according to intra prediction modes of neighboring blocks.

First, it may be determined whether the size of the current block corresponds to a predetermined size (S1410). The predetermined size may be determined by a horizontal length or a vertical length of the current block. For example, in step S1410, the determination may be made depending on whether the horizontal length or the vertical length of the current block is a partitionable length for partitioning into sub-blocks.

For example, in the case where the current block is a square having the same horizontal length as the vertical length, if a length obtained by dividing each of the horizontal length and the vertical length by N is equal to or greater than an arbitrary length, the size of the current block may correspond to the predetermined size. For example, in the case where N is 4 and the arbitrary length is 4, if the size of the current block is one of the sizes 256×256, 128×128, 64×64, 32×32, and 16×16, the size of the current block may correspond to the predetermined size.

For example, in the case where the current block is a rectangle having a horizontal length different from a vertical length, if a smaller one of a length obtained by dividing a larger one of the horizontal length and the vertical length by M and a length obtained by dividing a smaller one of the horizontal length and the vertical length by N is equal to or greater than an arbitrary length, the size of the current block may correspond to the predetermined size. For example, in the case where M is 4, n is 2, and the arbitrary length is 4, if the size of the current block is one of sizes 128×64, 64×128, 128×32, 32×128, 128×16, 16×128, 128×8, 8×128, 64×32, 32×64, 64×16, 16×64, 64×8, 8×64, 32×16, 16×32, 32×8, 8×32, 16×8, and 8×16, the size of the current block may correspond to the predetermined size.

For example, if the current block is not divided any more, the size of the current block may correspond to the predetermined size. For example, if the partition information, the quadtree partition information, and/or the binary tree partition information about the current block is 0, it is indicated that the current block is not partitioned, and the horizontal length or the vertical length of the current block is greater than the minimum length, the size of the current block may correspond to the predetermined size. Here, the minimum length may be 4.

If the size of the current block does not correspond to the predetermined size (no in S1410), the partition information and the intra prediction mode of the current block may be decoded (S1460). If the current block is not divided, an intra prediction mode of the current block may be decoded, and if the current block is divided into sub-blocks, an intra prediction mode of each sub-block may be decoded.

If the size of the current block corresponds to the predetermined size (yes in S1410), the ndip_flag may be decoded (S1420). In the next step, the decoded ndip_flag value may be checked (S1430).

If ndip_flag is 0 (no in S1430), at least one of partition information regarding the current block, an intra prediction mode of the current block, and an intra prediction mode of a sub-block may be decoded (S1460).

If the ndip_flag is 1 (yes in S1430), the current block may be divided into sub-blocks (S1440). Here, the division may be performed such that each of the sub-blocks has a predetermined size and/or shape. Alternatively, the division may be performed based on the decoded division information.

In the next step, an intra prediction mode of a sub-block generated by dividing the current block may be derived (S1450). Intra prediction modes of the sub-blocks may be inferred based on intra prediction modes of neighboring blocks. Alternatively, the intra prediction mode of the current block may be decoded and used.

Intra prediction may be performed using an intra prediction mode derived for the current block or sub-block (S1470).

The order in which the intra prediction modes of the plurality of sub-blocks in the current block are derived may be based on a raster scan order of the current block. Alternatively, the order may be a raster scan order based on a predetermined block size. For example, the intra prediction modes of the sub-blocks may be inferred in the order of C1, C2, C3, …, C16. Alternatively, the intra prediction modes of the sub-blocks may be inferred in the order of C1, C2, C5, C6, C3, C4, …, C12, C15, C16. Alternatively, the intra prediction mode of each sub-block may be derived in parallel. The intra prediction mode of each sub-block may be derived in at least one of methods for deriving the intra prediction mode of the current block.

For example, if a current block is divided into sub-blocks and an intra prediction mode for each sub-block is derived, intra prediction modes of neighboring blocks may be used.

For example, statistics of intra prediction modes of blocks left and above a sample at a position (0, 0) of each sub-block may be derived as intra prediction modes of the sub-block. For example, if the statistical value is a mean value, the intra prediction mode of each sub-block shown in fig. 15 may be derived by the following [ equation 4 ].

[ equation 4]

C1＝(j+d+1)>>1,

C2＝(C1+e+1)>>1,

C3＝(C2+g+1)>>1,

C4＝(C3+g+1)>>1,

C5＝(j+C1+1)>>1,

C6＝(C5+C2+1)>>1,

C7＝(C6+C3+1)>>1,

C8＝(C7+C4+1)>>1,

C9＝(k+C5+1)>>1,

C10＝(C9+C6+1)>>1,

C11＝(C10+C7+1)>>1,

C12＝(C11+C8+1)>>1,

C13＝(l+C9+1)>>1,

C14＝(C13+C10+1)>>1,

C15＝(C14+C11+1)>>1,

C16＝(C15+C12+1)>>1。

Alternatively, the sizes of the blocks left and above the sample at the position (0, 0) of each sub-block may be compared with each other, and the intra prediction mode of the block having the larger size may be derived as the intra prediction mode of the sub-block. If the two blocks have the same size, the mean of the intra prediction modes of the left block and the upper block may be derived as the intra prediction mode of the sub-block.

Alternatively, the sizes of the intra prediction modes of the blocks left and above the sample at the position (0, 0) of each sub-block may be compared with each other, and the intra prediction mode having a smaller value may be derived as the intra prediction mode of the sub-block. If the values of the two modes are equal, one of the two modes may be derived as an intra prediction mode for the sub-block.

Alternatively, the intra prediction mode of each sub-block may be derived using intra prediction modes of neighboring blocks of the current block. Here, intra prediction modes of one or more neighboring blocks of the current block to the left and/or above the sample position (0, 0) of each sub-block may be used. For example, the intra prediction mode of each sub-block shown in fig. 15 may be derived by the following [ equation 5 ].

[ equation 5]

C1＝(j+d+1)>>1,

C2＝e,

C3＝g,

C4＝g,

C5＝j,

C6＝(j+e+1)>>1,

C7＝g,

C8＝g,

C9＝k,

C10＝k,

C11＝(k+g+1)>>1,

C12＝g,

C13＝l,

C14＝l,

C15＝l,

C16＝(l+g+1)>>1。

Alternatively, if all intra prediction modes of neighboring blocks of the current block are non-directional modes, the intra prediction mode of the sub-block may be derived as at least one of non-directional modes (e.g., DC mode and planar mode).

As shown in fig. 16, the sub-blocks in the current block may vary in size and/or shape. The partition structure and/or size of the current block and/or sub-block may be determined by encoding/decoding. The intra prediction mode of each sub-block may be derived according to at least one of the methods for deriving the intra prediction mode of the current block or sub-block described previously.

For example, statistics of intra prediction modes of blocks left and above a sample at a position (0, 0) of each sub-block may be derived as intra prediction modes of the sub-block. For example, if the statistical value is a mean value, the intra prediction mode of the sub-block shown in fig. 16 may be derived by the following [ equation 6 ].

[ equation 6]

C1＝(j+d+1)>>1,

C2＝(C1+e+1)>>1,

C3＝(C2+g+1)>>1,

C4＝(k+C1+1)>>1,

C5＝(C4+C2+1)>>1,

C6＝(l+C4+1)>>1,

C7＝(C6+C5+1)>>1,

C8＝(C5+C3+1)>>1,

C9＝(C8+C3+1)>>1,

C10＝(C7+C8+1)>>1。

Alternatively, statistics of intra prediction modes of one or more neighboring blocks adjacent to each sub-block may be derived as intra prediction modes of the sub-block. For example, if the statistical value is a mean value, the intra prediction mode of each sub-block shown in fig. 16 may be derived by the following [ equation 7 ].

[ equation 7]

C1＝(b+j+d)/3,

C2＝(C1+d+e)/3,

C3＝(C2+e+g)/3,

C4＝(k+j+C1)/3,

C5＝(C4+C2+C1)/3,

C6＝(l+C4+k)/3,

C7＝(C6+C5+C4)/3,

C8＝(C5+C3+C2)/3,

C9＝(C8+C3)/2,

C10＝(C5+C8+C9+C7)/4。

In case that the current block is divided into sub-blocks and an intra prediction mode of each sub-block is derived, the intra prediction mode of the current block may be derived by the MPM, and then the intra prediction mode of each sub-block may be derived using the derived mode and the intra prediction modes of neighboring blocks. Here, the intra prediction mode of the sub-block may be inferred using at least one of the intra prediction mode of the current block and the intra prediction mode of the neighboring block, which are inferred by MPM, according to at least one of the methods for deriving the intra prediction mode of the current block. If the intra prediction mode of the current block, which is derived by the MPM, is pred_mpm, the intra prediction mode of the sub-block may be inferred in the following manner.

For example, the mean value of intra prediction modes of blocks left and above the sample point at the position (0, 0) of each sub-block is compared with pred_mpm. Pred_mpm+1 may be derived as an intra prediction mode of a sub-block if the average is greater than Pred_mpm, and Pred_mpm-1 may be derived as an intra prediction mode of a sub-block if the average is less than Pred_mpm. Alternatively, the average value of intra prediction modes of blocks left and above the sample at the position (0, 0) of each sub-block and pred_mpm may be derived as the intra prediction modes of the sub-blocks. Alternatively, the intra prediction mode of the sub-block may be inferred by comparing the intra prediction modes of the blocks left and above the samples at the position (0, 0) of each sub-block with pred_mpm and adjusting pred_mpm. Here, at least one of the foregoing statistics may be used instead of the average.

In fig. 17, the number marked on each block indicates the number of the intra prediction mode of the block. Further, cx (x is 1, …, 16) represents the x-th sub-block of the current block. Further, the arrow indicates the direction or angle of the intra prediction mode of the block.

For example, statistics of intra prediction modes of blocks left and above a sample at a position (0, 0) of each sub-block may be derived as intra prediction modes of the sub-block. The statistic may be, for example, a mean value. Alternatively, if at least one of the intra prediction modes of the neighboring block is a non-directional mode, the intra prediction mode of the sub-block may be derived as a directional mode among the intra prediction modes of the neighboring block. The non-directional modes may include, for example, a planar mode (mode number 0) and a DC mode (mode number 1). For example, the intra prediction mode of each sub-block shown in fig. 17 may be derived by the following [ equation 8 ].

[ equation 8]

C1＝(30+50+1)>>1＝40

C2＝(40+50+1)>>1＝45

C3＝45

C4＝(45+58+1)>>1＝52

C5＝(18+40+1)>>1＝29

C6＝(29+45+1)>>1＝37

C7＝(37+45+1)>>1＝41

C8＝(41+52+1)>>1＝47

C9＝(16+29+1)>>1＝23

C10＝(23+37+1)>>1＝30

C11＝(30+41+1)>>1＝36

C12＝(36+47+1)>>1＝42

C13＝23

C14＝(23+30+1)>>1＝27

C15＝(27+36+1)>>1＝32

C16＝(32+42+1)>>1＝37

In fig. 18, the number marked on each block indicates the number of the intra prediction mode of the block. Further, cx (x is 1, …, 14) represents the x-th sub-block of the current block. Furthermore, the arrow indicates the direction or angle of intra prediction of the block.

In the embodiment described with reference to fig. 18, at least one of the intra prediction mode of the current block and the partition information of the sub-block may be derived by decoding. The intra prediction mode of each sub-block in the current block may be derived using the derived intra prediction mode of the current block and the average of the intra prediction modes of the blocks left and above the sample point at the position (0, 0) of each sub-block. For example, if the derived intra prediction mode of the current block is greater than the mean value, 1/2 of the mean value may be subtracted from the derived intra prediction mode. If the derived intra prediction mode of the current block is equal to or less than the mean value, 1/2 of the mean value may be added to the derived intra prediction mode. Here, at least one of the aforementioned statistics values may be used instead of the mean value.

Alternatively, if at least one of the intra prediction modes of the neighboring block is a non-directional mode, the intra prediction mode of the sub-block may be derived as a directional mode among the intra prediction modes of the neighboring block. The non-directional modes may include, for example, a planar mode (mode number 0) and a DC mode (mode number 1). For example, if the derived intra prediction mode of the current block is 52, the intra prediction mode of each sub-block shown in fig. 18 may be derived by the following [ equation 9 ].

[ equation 9]

C1:abs(52-((30+50+1)>>1)+1)>>1＝6,C1＝52-6＝46

C2:abs(52-((46+50+1)>>1)+1)>>1＝2,C2＝52-2＝50

C3:abs(52-((50+64+1)>>1)+1)>>1＝3,C3＝52+3＝55

C4:abs(52-((18+46+1)>>1)+1)>>1＝10,C4＝52-10＝42

C5:abs(52-((42+50+1)>>1)+1)>>1＝3,C5＝52-3＝49

C6:abs(52-((42+49+1)>>1)+1)>>1＝3,C6＝52-3＝49

C7:abs(52-((49+55+1)>>1)+1)>>1＝0,C7＝52-0＝52

C8:abs(52-((52+55+1)>>1)+1)>>1＝1,C8＝52+1＝53

C9:abs(52-((16+42+1)>>1)+1)>>1＝12,C9＝52-12＝40

C10:abs(52-((16+40+1)>>1)+1)>>1＝12,C10＝52-12＝40

C11:abs(52-40+1)>>1＝6,C11＝52-6＝46

C12:abs(52-((40+49+1)>>1)+1)>>1＝4,C12＝52-4＝48

C13:abs(52-((48+49+1)>>1)+1)>>1＝2,C13＝52-2＝50

C14:abs(52-((50+52+1)>>1)+1)>>1＝1,C14＝52-1＝51

To derive the intra-prediction mode, information about the intra-prediction may be decoded (e.g., entropy decoded) from the bitstream. Information about intra prediction may be signaled in at least one of VPS (video parameter set), SPS (sequence parameter set), PPS (picture parameter set), APS (adaptive parameter set), slice header, parallel block header, CTU, CU, and PU. The information on intra prediction may include at least one of the following pieces of information.

-a flag indicating whether reference sample filtering is applied: for example, intra_reference_sample_filtering_flag

-an index indicating the type of reference sample filtering: for example, reference_sample_filtering_idx

-a flag indicating whether MPM (most probable mode) matches: for example, prev_intra_luma_pred_flag

-an index indicating a position in the MPM list: for example mpm_idx

-a flag indicating whether an intra prediction mode is included in a set of predetermined modes of the non-MPM modes: for example non-mpm group flag

-an index indicating the positions in the set: for example, group_mode_idx

Intra prediction mode information on luminance component: for example, rem_intra_luma_pred_mode

Intra prediction mode information on chroma components: for example, intra_chroma_pred_mode

Curvature parameters of the point-by-point directional intra prediction mode: for example, cuv

-a set of row and/or column weight parameters for a point-by-point directional intra prediction mode: for example, cw1, cw2, …, cWNs-1

Look-up table (LUT) for intra-prediction of direction from sample to sample

-a flag indicating the use of intra prediction modes of neighboring blocks to derive intra prediction modes of the current block and sub-block: for example, NDIP_flag

-a flag indicating that filtering is applied to the predicted samples: for example, predicted_sample_filtering_flag

Decoding of information regarding intra prediction may be performed based on at least one encoding parameter. For example, encoding/decoding of the ndip_flag may be performed based on information related to the block division information. For example, if at least one of the split_ flag, quadtree _flag and the binaryrate_flag is 0, that is, if the block is no longer divided, encoding/decoding of the ndip_flag may be performed.

For the case where the block size is equal to or smaller than the predetermined block size, at least one piece of information regarding intra prediction may not be signaled. For example, if the size of the current block corresponds to a predetermined size, one or more pieces of information regarding intra prediction for the current block may not be signaled, and one or more pieces of information regarding intra prediction for a previously encoded/decoded larger-sized block may be used.

In entropy encoding/entropy decoding at least one piece of information regarding intra prediction, at least one of the following binarization methods may be used.

-truncated rice binarization method

K-order exponential golomb binarization method

-finite K-order exponential golomb binarization method

Fixed length binarization method

-unitary binarization method

-truncated unary binarization method

If the MPM (most probable mode) flag is 1, at least one of the intra prediction modes of the neighboring units that have been encoded/decoded and the MPM index (mpm_idx) may be used to derive the intra-luminance prediction mode.

If the MPM (most probable mode) flag is 0, a flag indicating whether the intra prediction mode is included in a set of predetermined modes among the non-MPM modes is parsed. If the parsed flag is 1, a group mode index (group_mode_idx) may be used to derive an intra prediction mode.

If at least one of an MPM (most probable mode) flag and a flag indicating whether an intra prediction mode is included in a set of predetermined modes among non-MPM modes is 0, the intra luminance prediction mode may be encoded/decoded using an intra luminance prediction mode index (rem intra luma pred mode).

The intra chroma prediction mode may be derived using at least one of an intra chroma prediction mode index (intra chroma pred mode) and/or an intra prediction mode of the corresponding luma block. Alternatively, the MPM list may be made using at least one of an intra prediction mode adjacent to the chroma block, an intra prediction mode of a corresponding luma block and an intra prediction mode adjacent to the luma block, and a predetermined intra prediction mode, and the intra chroma prediction mode may be derived using the MPM list.

The curvature parameter (cuv) of the progressive directional intra prediction mode may refer to a curvature applied to the progressive directional intra prediction mode. The point-by-point directional intra prediction may be performed for the current block using at least one cuv. The curvature parameter may be derived from curvature parameters of neighboring blocks.

The set of row and/or column weight parameters (cw) for the point-wise directional intra-prediction mode may be vectors. The row and/or column weight parameters may be applied on a row and/or column basis in the current block. For example, in the case of a progressive application to an nxm block, the set of row weight parameters may have N weight parameters. Furthermore, in the case of a column-wise application, the column weight parameter set may have M weight parameters. The weight parameters and/or weight parameter sets may be derived from weight parameters and/or weight parameter sets of neighboring blocks.

Various types of sample-by-sample intra prediction may be performed using at least one of cuv and cw. Here, the number of each of cuv and cw may be 1 or more.

Intra prediction may be performed for a current block by generating at least nxmx 4 prediction blocks using N cuvs and M cw. For example, intra prediction may be performed for a current block by generating at least 4 prediction blocks using 1 cuv and 1 cw. For example, intra prediction may be performed for a current block by generating at least 8 prediction blocks using 2 cuv and 1 cw.

Two or more pieces of cuv and/or cw information may be encoded/decoded using default values and delta values. Here, the default value may refer to a cuv value and/or a cw value, and the increment value may be constant.

For example, if two cuvs are used for the current block, then default_cuv and delta_cuv may be decoded from the bitstream. Here, the two curvature parameters may be default_cuv and default_cuv+delta_cuv.

For example, if N cuvs are used for the current block, default_cuv and delta_cuv may be decoded from the bitstream. Here, the N curvature parameters may be default_cuv, default_cuv+delta_cuv, default_cuv+2×delta_cuv, …, default_cuv+ (N-1) ×delta_cuv (N is a positive integer equal to or greater than 2).

For example, if 2n+1 cuvs are used for the current block, the 2n+1 curvature parameters may be default_cuv, default_cuv+delta_cuv, default_cuv-delta_cuv, default_cuv+2 x delta_cuv, default_cuv-2 x delta_cuv, …, default_cuv+n x delta_cuv, default_cuv-N x delta_cuv (N is a positive integer equal to or greater than 2).

For example, if 2 cws are used for the current block, default_cws and delta_cws may be decoded from the bitstream. Here, the 2 weight parameters may be default_cw and default_cw+delta_cw (default_cw+delta_cw is addition at vector element level).

For example, if M cw are used for the current block, default_cw and delta_cw may be decoded from the bitstream. Here, the M weight parameters may be default_cw, default_cw+delta_cw, default_cw+2×delta_cw, …, default_cw+ (M-1) ×delta_cw (default_cw+delta_cw is an addition at vector element level, and M is a positive integer equal to or greater than 2).

For example, if 2m+1 cws are used for the current block, the 2m+1 curvature parameters may be default_cw, default_cw+delta_cw, default_cw-delta_cw, default_cw+2 x delta_cw, default_cw-2 x delta_cw, …, default_cw+m x delta_cw, default_cw-M x delta_cw (M is a positive integer equal to or greater than 1).

Now, a detailed description will be given of the reference point constructing step S1220.

In intra prediction of a current block or a sub-block having a smaller size and/or shape than the current block, a reference sample may be constructed for prediction. The following description is given in the context of the current block, and the current block may mean a sub-block. The reference samples may be constructed using one or more reconstructed samples or a combination of samples adjacent to the current block. Furthermore, filtering may be applied when constructing the reference samples. Here, the reference sample point may be constructed using each reconstructed sample point on the plurality of reconstructed sample points as it is. Alternatively, the reference samples may be constructed after filtering between samples on the same reconstructed sample line. Alternatively, the reference samples may be constructed after filtering between samples on different reconstructed sample lines. The constructed reference samples may be represented by ref [ m, n ], and the reconstructed neighboring samples or samples obtained by filtering the reconstructed neighboring samples may be represented by rec [ m, n ]. Here, m or n may be a predetermined integer value. In the case where the size of the current block is W (horizontal) ×n (vertical), the relative position of the leftmost reference sample closest to the leftmost sample if the leftmost sample of the current block is (0, 0) may be set to (-1, -1).

As shown in fig. 19, one or more reconstructed sample lines adjacent to the current block may be used to construct a reference sample.

For example, one of the plurality of reconstructed sample lines shown in fig. 19 may be selected, and the reference sample point may be constructed using the selected reconstructed sample line. A predetermined reconstructed sample line of the plurality of reconstructed sample lines may be fixedly selected as the selected reconstructed sample line. Alternatively, a particular reconstructed sample line of the plurality of reconstructed sample lines may be adaptively selected as the selected reconstructed sample line.

For example, one or more of the plurality of reconstructed sample lines shown in fig. 19 may be used in combination to construct a reference sample. For example, the reference sample may be constructed as a weighted sum (or weighted average) of one or more reconstructed samples. The weights for the weighted sum may be assigned based on the distance from the current block. Here, a distance closer to the current block may be assigned a larger weight. For example, the following [ equation 10] may be used.

[ equation 10]

ref[-1,-1]＝(rec[-2,-1]+2*rec[-1,-1]+rec[-1,-2]+2)>>2

ref[x,-1]＝(rec[x,-2]+3*rec[x,-1]+2)>>2,(x＝0～W+H-1)

ref[-1,y]＝(rec[-2,y]+3*rec[-1,y]+2)>>2,(y＝0～W+H-1)

Alternatively, the reference samples may be constructed using at least one of a mean, a maximum, a minimum, a median, and a most frequent value of the plurality of reconstructed samples based on at least one of a distance from the current block or an intra prediction mode.

Alternatively, the reference samples may be constructed based on changes (variations) in the values of a plurality of successive reconstructed samples. For example, the reference sample point may be constructed based on at least one of: whether the difference between the values of two consecutive reconstructed samples is equal to or greater than a threshold value, whether the values of the two consecutive reconstructed samples change continuously or discontinuously, and so on. For example, if the difference between rec < -1 > and rec < -2 > -1 > is equal to or greater than a threshold value, ref < -1 > may be determined as rec < -1 > or a value obtained by applying a weighted average value using a predetermined weight assigned to rec < -1 >. For example, if the values of a plurality of consecutive reconstructed samples change by n each time as the plurality of consecutive reconstructed samples approach the current block, the reference samples ref [ -1, -1] may be determined as rec [ -1, -1] -n.

For example, the reference sample point may be constructed by selecting two or more of the plurality of reconstructed sample points shown in fig. 19. For example, the reconstructed sample line 1 and the reconstructed sample line 2 may be fixedly selected. Alternatively, two or more reconstructed sample lines may be adaptively selected. Alternatively, one line may be fixedly selected and one or more other lines may be adaptively selected.

If one or more of the plurality of reconstructed sample lines are fixedly selected, information about the fixedly selected lines may not be signaled.

If one or more of the plurality of reconstructed sample lines are adaptively selected, information about the adaptively selected lines may be signaled. The information may be, for example, an indicator or index indicating the adaptively selected line. Alternatively, the one or more reconstructed sample lines may be adaptively selected using at least one of the size, shape, and intra prediction mode of the current block and/or neighboring blocks without signaling information.

One or more sample points may be used to construct a reference sample point line. For example, the length of the reference sample line may be constructed to be the same as the horizontal length or the vertical length of the current block. Alternatively, the reference sample line may be constructed to be twice the horizontal length or the vertical length of the current block. Alternatively, the reference sample line may be constructed as a length obtained by adding 1, 2, 3, …, N samples to the horizontal length or the vertical length of the current block. For example, 2 x (w+h) +n spots can be used to construct a reference spot line.

The number of adjacent reference sample lines above the current block may be different from the number of adjacent reference sample lines to the left of the current block. For example, one adjacent reference sample line may be constructed above the current block and two adjacent reference sample lines may be constructed at the left side of the current block according to the size, shape, and/or intra prediction mode of the current block.

The length of the neighboring reference sample line above the current block may be different from the length of the neighboring reference sample line to the left of the current block. For example, the length may be different according to the size, shape, and/or intra prediction mode of the current block.

The length of the reference sample line may be different for each reconstructed sample line. For example, the reconstructed sample line n may be constructed to be m sample points longer or shorter than the reconstructed sample line n-1. In the example shown in fig. 19, the reconstructed sample line n is constructed to be one sample longer than the reconstructed sample line n-1.

Alternatively, each of the reference sample lines may be reconstructed by shifting according to the intra prediction mode. For example, in the absence of a reference sample point at a location referenced by the intra-prediction mode, the corresponding reference sample line may be shifted such that there may be a reference sample point at that location. Which reference sample line is to be shifted or by how much may be determined based on the intra-prediction mode, the prediction angle, and/or the position of the reference sample line.

As described above, information indicating whether to construct a reference sample point using only the closest reference sample point line or using a plurality of reference sample point lines can be encoded/decoded. For example, the information may be encoded/decoded in at least one of a sequence level, a picture level, a slice level, a parallel block level, a CTU level, a CU level, a PU level, and a TU level. Further, information about the availability of multiple reference sample lines may be signaled at a higher level.

At least one of the number, position, and construction method of the plurality of reconstructed sample lines for constructing the reference sample points may be changed according to the following cases: the upper boundary and/or the left boundary of the current block corresponds to a boundary of at least one of a picture, a slice, a parallel block, and a CTB. For example, in case that two or more reference sample lines are constructed, if an upper boundary of a current block corresponds to a boundary of at least one of a picture, a slice, a parallel block, and a CTB, n upper neighboring reference sample lines may be constructed. Here, n may be, for example, 1.

In selecting the reference sample point, a decision regarding availability of the block including the reference sample point and/or a padding may be performed. For example, if a block including a reference sample is available, the reference sample may be used. Meanwhile, if a block including a reference sample is not available, the unavailable reference sample may be replaced by one or more available neighboring reference samples by padding.

If the reference sample point exists outside at least one boundary among the picture boundary, the parallel block boundary, the slice boundary, the CTB boundary, and the predetermined boundary, it may be determined that the reference sample point is not available.

In the case of encoding a current block by CIP (constrained intra prediction), if a block including a reference sample is encoded/decoded in an inter prediction mode, it may be determined that the reference sample is not available.

If it is determined that a neighboring reconstructed sample is not available, the neighboring available reconstructed sample may be used to replace the unavailable sample. For example, as shown in fig. 20, in the case where there are available and unavailable spots, one or more available spots may be used to replace the unavailable spot.

The sample values of the unavailable samples may be replaced with the sample values of the available samples in a predetermined order. Available samples adjacent to an unavailable sample may be used to replace the unavailable sample. In the absence of adjacent available samples, the available sample that appears first or the closest available sample may be used. The order of replacement of unavailable samples may be from bottom left-most to top right-most. Alternatively, the order of replacement of unavailable samples may be from the top right to the bottom left. Alternatively, the replacement order of unavailable samples may be an order from top left-most to top right-most and/or bottom left-most. Alternatively, the replacement order of unavailable samples may be an order from top right and/or bottom left to top left.

As shown in fig. 20, the unusable samples may be replaced in order from the bottom-left-most sample position 0 to the top-right-most sample. In this case, the values of the first four unavailable samples may be replaced with the value of the first occurring or closest available sample a. The value of the last available sample b can be used to replace the value of the next 13 unavailable samples.

Alternatively, combinations of available samples may be used to replace unavailable samples. For example, the unavailable sample may be replaced with the average of available samples adjacent to both ends of the unavailable sample. For example, in fig. 20, the first four unavailable samples may be filled with the value of available sample a, and the next 13 unavailable samples may be filled with the average of available sample b and available sample c. Alternatively, the 13 unavailable samples may be filled with any value between the values of available sample b and available sample c. In this case, the unavailable samples may be replaced with different values. For example, as an unavailable sample approaches available sample a, the value of the unavailable sample may be replaced with a value that is close to the value of available sample a. Similarly, as an unavailable sample approaches available sample b, the value of the unavailable sample may be replaced with a value that is close to the value of available sample b. That is, the value of the unavailable spot may be determined based on the distance from the unavailable spot to the available spots a and/or b.

To replace the unavailable spot, one or more of a plurality of methods including the above method may be selectively applied. The method for replacing the unavailable samples may be signaled by information included in the bitstream, or a method predetermined by an encoder and a decoder may be used. Alternatively, the method for replacing unavailable samples may be derived by a predetermined mechanism. For example, the method for replacing the unavailable sample point may be selected based on the difference between the values of the available sample point a and the available sample point b and/or the number of unavailable sample points. For example, a method for replacing an unavailable sample may be selected based on a comparison between a difference between values of two available samples and a threshold and/or a comparison between a number of unavailable samples and a threshold. For example, if the difference between the values of two available samples is greater than a threshold and/or the number of unavailable samples is greater than a threshold, the value of the unavailable sample may be replaced with a different value.

The method for replacing unavailable samples may be selected on a predetermined unit basis. For example, a method for replacing unavailable samples may be selected based on at least one of, for example, video, sequence, picture, slice, parallel block, CTU, CU, PU, and TU. Here, the selection of the method for replacing the unavailable samples may be based on information signaled on a predetermined unit basis or may be derived on a predetermined unit basis. Alternatively, a method predetermined by the encoder and the decoder may be applied.

For reference samples at predetermined locations, padding may be performed without a decision regarding the availability of blocks including the reference samples. For example, in the example shown in fig. 19, adjacent reference samples may be used to fill reference samples located at a position greater than the length w+h without the need for an availability determination. For example, the sample ref [ W+H, -2] may be filled with the value of ref [ W+H-1, -2] without the need for availability determination. Alternatively, the samples ref [ W+H, -3] and ref [ W+H+1, -3] may be filled with the values of ref [ W+H-1, -3] without the need for availability determination.

Among reference samples above the current block that are outside the horizontal length of the current block, the usability determination and/or padding may be performed for as many samples as the vertical length of the current block. Meanwhile, among reference samples to the left of the current block, which are outside the vertical length of the current block, the usability determination and/or padding may be performed for as many samples as the horizontal length of the current block. For example, the availability determination and/or filling may be performed for reference samples corresponding to rec [ x, -1] (x= -1-w+h-1) and/or rec [ -1, y ] (y=0-h+w-1).

For the constructed one or more reference samples, whether to apply filtering and/or a type of filtering may be determined in different ways based on at least one of an intra prediction mode, a size, and/or a shape of the current block. For a plurality of reference sample lines, for example, whether to apply filtering may be determined differently. For example, filtering may be applied to a first adjacent reference sample line and filtering may not be applied to a second adjacent reference sample line.

Further, for example, both filtered and unfiltered values may be used for the same reference sample. For example, at least one different filter of a 3-tap filter, a 5-tap filter, a 7-tap filter, and an N-tap filter may be selected and applied according to at least one of an intra prediction mode and a size and/or shape of the current block. Here, N may be an integer.

Different filter shapes may be selected and applied according to at least one of an intra prediction mode and a size and/or shape of the current block. The filter shape may be one-dimensional or two-dimensional. Fig. 21 is an exemplary view showing various two-dimensional filter shapes.

The shape of the current block may be judged or determined by comparing the horizontal length and the vertical length of the current block. For example, in the case where the horizontal length is greater than the vertical length and the horizontal length is less than the vertical length, at least one of the following may be variously applied: whether filtering is applied and/or the filter type. Alternatively, whether filtering and/or filter type are applied may be applied differently depending on whether the horizontal length and the vertical length are equal or different.

Now, a detailed description will be given of the step of performing intra prediction (S1230).

Intra prediction may be performed on the current block or sub-block based on the derived intra prediction mode and the reference sample point. In the following detailed description, a current block may mean a sub-block.

For example, non-directional intra prediction may be performed as intra prediction. The non-directional mode may be, for example, at least one of a DC mode and a planar mode.

If the non-directional mode is a DC mode, intra prediction may be performed using a mean of one or more of the constructed reference samples. Here, filtering may be applied to one or more prediction samples located at the boundary of the current block. The number of means may be 1 or more, and prediction may be performed using different means according to the position of the target sample for prediction. Different reference samples may be used according to at least one of the size or shape of the current block. For example, if the size of the block is greater than a predetermined size, one adjacent reference sample line may be used, and if the size of the block is less than the predetermined size, two adjacent reference sample lines may be used.

If the non-directional mode is a planar mode, intra prediction may be performed using a weighted sum calculated considering distances from one or more reference samples constructed according to the position of a target sample for intra prediction in the current block.

For example, directional intra prediction may be performed as intra prediction. The direction mode may be, for example, at least one of a horizontal mode, a vertical mode, and a mode having a predetermined angle.

If the direction mode is a horizontal mode and/or a vertical mode, intra prediction may be performed using at least one reference sample located on a horizontal line and/or a vertical line of a position of a target sample for intra prediction.

If the direction mode is a mode having a predetermined angle, intra prediction may be performed using one or more samples located on a line at a predetermined angle with respect to a position of a target sample for intra prediction and adjacent to the line. Here, N reference samples may be used. N may be a positive integer such as 2, 3, 4, 5, and 6, and intra prediction may be performed by applying N tap filters (such as 2 tap filter, 3 tap filter, 4 tap filter, 5 tap filter, and 6 tap filter). Here, one or more reference sample points may be used, and a different filter type may be applied to each reference sample point line. Intra prediction may be performed by calculating a weighted average of values obtained by applying a filter to each line. The number of reference sample lines for direction prediction may be different according to at least one of a direction mode, a size of a current block, and a shape of the current block.

Alternatively, intra prediction may be performed based on the location information. The location information may be encoded/decoded, and the reconstructed sample block located at the location may be derived as an intra-prediction block for the current block. Alternatively, a block similar to the current block searched by the decoder may be derived as an intra prediction block of the current block.

Alternatively, intra prediction may be performed based on a luminance signal and/or a chrominance signal. For example, intra prediction for a chrominance signal may be performed using a reconstructed luminance signal of a current block. For example, intra prediction for another chroma signal Cr may be performed using one reconstructed chroma signal Cb of the current block.

Intra prediction may be performed by using one or more of the above-described various intra prediction methods in combination. For example, an intra-prediction block may be constructed for a current block by a weighted sum of a block predicted using a predetermined non-directional intra-prediction mode and a block predicted using a predetermined directional intra-prediction mode. Here, different weights may be applied according to at least one of an intra prediction mode, a block size, a shape, and/or a sample position of the current block.

Alternatively, regarding the combined use of the one or more intra prediction modes, a prediction block may be constructed using a weighted sum of a value predicted using the intra prediction mode of the current block and a value predicted using a predetermined mode included in the MPM list.

Alternatively, frame prediction may be performed using one or more sets of reference samples. For example, intra prediction may be performed for a current block using a block predicted intra using a reference sample obtained by not applying filtering to a constructed reference sample and using a weighted sum of blocks predicted intra using a reference sample obtained by applying filtering to a constructed reference sample.

In the processing of intra prediction, a filtering operation may be performed using neighboring reconstructed samples. Here, the filtering operation may be performed according to at least one of an intra prediction mode, a block size, a shape, and/or a sample position of the current block or may not be performed according to at least one of an intra prediction mode, a block size, a shape, and/or a sample position of the current block. The filtering operation may be included in the intra prediction process and thus may be performed as one step.

In an operation of performing intra prediction by dividing a current block into sub-blocks and deriving an intra prediction mode of each sub-block using intra prediction modes of neighboring blocks, filtering may be applied to each sub-block of the current block. For example, a low pass filter may be applied to the entire current block. Alternatively, a filter may be applied to samples located at the boundary of each sub-block. Alternatively, a filter may be applied to the prediction block or the reconstruction block of each sub-block, and one or more samples of the sub-block to which the filter is applied may be used in intra prediction of a subsequent sub-block.

In the operation of dividing the current block into sub-blocks and performing intra prediction for each sub-block, each sub-block may refer to at least one of an encoding block/decoding block, a prediction block, and a transform block. For example, if the size of the current block is 64×64 and the size of the sub-block is 16×16, an intra prediction mode, which is a prediction block of each sub-block, may be derived and/or the intra prediction may be performed with respect to the prediction block. If each of one or more sub-blocks is further divided into 8×8 or 4×4 blocks, each of the 8×8 or 4×4 blocks may be a transform block, and intra prediction may be performed on a block obtained by the further division using an intra prediction mode of the 16×16 block.

In directional intra prediction, at least one of N directional modes may be used to encode/decode a current block. Here, N may be a positive integer such as 33 or 65.

In the example shown in fig. 22, N is 33, and for each intra prediction mode (preModeIntra), an example of an angle (intraPredAngle) between each direction mode and the vertical direction is shown.

In directional intra prediction, a current block may be encoded/decoded in one or more of M sample-by-sample directional modes, M being a positive integer. The sample-by-sample directional mode may refer to a mode in which prediction is performed for each target sample or multiple target samples for prediction in the current block using the one or more directional intra-prediction modes.

Parameters for determining the number of sample-by-sample directional patterns may be used. For example, a curvature parameter (cuvN) and/or a set of weight parameters (cWN [ i ]]、i＝0、...、N _S At least one of 1) may be used as said parameter.

For example, in the mode 35 of fig. 22, various sample-by-sample direction prediction blocks may be generated by a combination of two parameters in a direction from the rightmost upper to leftmost lower. In the mode 36 of fig. 22, for example, various sample-by-sample direction prediction blocks can be generated by a combination of two parameters in the direction from the leftmost upper to the rightmost lower. The curvature parameter and the weight parameter set are merely embodiments, and thus, various parameters may be used to generate a point-by-point direction prediction block. For example, for different block sizes, a look-up table may be commonly used between the encoder and decoder, wherein the look-up table lists the angles for detecting the locations of the reference samples for sample-by-sample directional prediction at each sample. Here, index information for referencing the lookup table may be encoded/decoded.

In directional intra prediction, a constructed reference sample may be reconstructed from the directional prediction modes. For example, if the direction prediction mode is a mode in which both the left reference sample and the upper reference sample are used, a unidirectional array may be constructed with the left reference sample or the upper reference sample.

For example, as shown in fig. 23, one or more of the left hand reference points may be used to construct a 1D array of upper reference points. Depending on the orientation pattern, different points other than the left hand point may be used to construct the upper reference point. The upper reference sample may be constructed by moving the left reference sample, or the upper reference sample may be constructed by using a weighted sum of one or more left reference samples.

In directional intra prediction, real-based interpolation prediction may be performed. For example, an offset (iIdx) and/or a weight (iFact) for predicting interpolation of a sample may be determined according to the position of the sample in the current block based on an angle parameter (inprepagle) corresponding to each direction prediction mode as follows.

For example, assuming that interpolation is performed in units of 1/32 pixel, the offset and weight of the direction pattern having the vertical direction can be determined by [ equation 11] below.

[ equation 11]

iIdx＝((y+1)*intraPredAngle)＞＞5

iFact＝((y+1)*intraPredAngle)&31

Can be according to [ equation 11]]The value of iFact in (c) to determine the different predicted sample values. For example, if iFact is not 0, reference point P _1，ref The predicted position in (a) is not an integer-based position (an integer point position), but a real-number-based position. Thus, the following [ equation 12] can be followed]A plurality of reference samples (e.g., two left-hand neighboring reference samples and a right-hand neighboring reference sample) adjacent to the real position are used to generate a predicted sample value at the target sample position (x, y). Here, the plurality of adjacent reference samples may be 4 or 6 left-side adjacent reference samples and right-side adjacent reference samples.

[ equation 12]

predSamples[x][y]＝((32-iFact)*p _1，ref [x+iIdx+1]+iFact*p _1，ref [x+iIdx+2]+16)＞＞5

For example, if iFact is 0, it can be obtained by the following [ equation 13]To generate predicted sample values. Alternatively, reference point P may be used _1,ref And the left and right reference samples apply 3 taps [1/4:2/4:1/4]A filter.

[ equation 13]

predSamples[x][y]＝p _1ref [x+iIdx+1]

In case of at least one of the horizontal mode and/or the vertical mode among the direction prediction modes, filtering may not be performed on the reference samples. Furthermore, interpolation prediction may not be required for reference samples. Furthermore, since prediction may only be possible with the upper reference sample or the left reference sample, a process of constructing a 1D array of reference samples may not be required.

As shown in fig. 24, the units of the direction mode may be changed according to the direction intra prediction. That is, prediction may be performed using one or more direction modes based on at least one of a sample point, a sample point group, and a unit of line in a target block.

For example, prediction may be performed based on the current block using a directional mode. Alternatively, prediction may be performed using direction prediction for each target sample line for prediction in the current block. That is, prediction may be performed using a different directional pattern for each line of at least one line among horizontal lines or vertical lines of the current block. Alternatively, the prediction may be performed using a direction mode for each predetermined target sample group for prediction in the current block. That is, prediction may be performed using a different direction mode for each group including N samples in the current block. For example, prediction may be performed using a direction mode for each target sample for prediction in the current block. That is, prediction may be performed using a different direction mode for each target sample for prediction in the current block.

Fig. 24 (a) shows an exemplary case where a different direction pattern is used for each sample in the target block. In the example shown in fig. 24 (a), a predicted value may be generated for each sample using a reference sample at an angle of each direction pattern.

Fig. 24 (b) shows an exemplary case where a different direction pattern is used for each horizontal line in the target block. In the example shown in fig. 24 (b), a predicted value may be generated for each horizontal line using a reference sample point at an angle of each direction pattern.

Fig. 24 (c) shows an exemplary case where a different direction pattern is used for each vertical line in the target block. In the example shown in (c) of fig. 24, a predicted value may be generated for each vertical line using a reference sample point at an angle of each direction pattern.

Fig. 24 (d) shows an exemplary case where a different direction pattern is used for each sample group in each diagonal direction in the target block. In the example shown in (d) of fig. 24, a predicted value may be generated for each diagonal sample group in terms of a diagonal direction using reference samples at angles of each direction pattern.

Fig. 24 (e) shows an exemplary case where a different direction pattern is used for each L-shaped line in the target block. In the example shown in fig. 24 (e), a predicted value may be generated for each right angle line using a reference sample point of the angle located in each direction pattern.

In addition to the example of fig. 24, various methods for grouping one or more samples may be possible. For example, a different direction pattern may be applied to each block generated by dividing latitude and/or longitude by any number.

If a sample-by-sample direction prediction is performed, N (N is a positive integer) direction prediction modes or angles available for at least one of the samples, the sample groups, and the units of lines may be stored in a table (such as a LUT) and subsequently used.

If the sample-by-sample direction prediction is performed, a different scanning method may be applied in the operation of scanning transform coefficients of a residual block for a target block according to at least one of a type, a block size, and/or a block shape of the sample-by-sample direction prediction. For example, the scanning may be performed using at least one of an up-right scan, a vertical scan, a horizontal scan, and a zig-zag scan according to the type of the sample-by-sample direction prediction.

Now, a description will be given regarding intra prediction of a chrominance component. For example, inter-color component intra-prediction may be performed for intra-prediction with respect to chroma components. Alternatively, intra chroma prediction may be performed using the reconstructed luma component of the current block. Alternatively, intra prediction for another chroma component Cr may be performed using one reconstructed chroma component Cb of the current block.

In inter-color intra prediction, a color component may refer to at least one of a luminance signal, a chrominance signal, red, green, blue, Y, cb, and Cr. In the prediction of the first color component, at least one of the second color component, the third color component, and the fourth color component may be used. Here, the color component signal used in the prediction may be at least one of an original signal, a reconstructed signal, a residual signal, and a predicted signal.

For example, in prediction of a target block of a second color component, intra prediction may be performed using at least one of samples of a corresponding block of a first color component corresponding to the target block and/or samples of neighboring blocks of the corresponding block.

For example, in prediction of the chrominance component block Cb or Cr, intra prediction may be performed using the reconstructed luminance component block Y corresponding to the chrominance component block.

For example, in predicting the second chrominance component block, the first chrominance component block corresponding to the block may be used. For example, a Cb component block may be used in the prediction of a Cr chroma block.

For example, at least one of the first, second and third color component blocks may be used in combination when predicting the fourth color component block.

It may be determined whether to perform inter-color intra prediction based on at least one of a size and a shape of the current target block.

For example, if the size of the target block is equal to a predetermined size, equal to or greater than the predetermined size, or corresponds to a predetermined size range, inter-color intra prediction may be performed. The predetermined size may be, for example, a CTU size.

For example, if the shape of the target block corresponds to a predetermined shape, inter-color intra prediction may be performed. For example, if the shape of the target block is square, inter-color intra prediction may be performed. Alternatively, if the shape of the target block is rectangular, inter-color intra prediction may not be performed.

Whether to perform inter-color intra prediction may be determined according to coding parameters of at least one of a corresponding block corresponding to a target block for prediction and neighboring blocks of the corresponding block.

For example, if the encoding mode of the corresponding block is an inter mode, inter intra prediction may not be performed. Alternatively, in the prediction of the second color component target block in a CIP (constrained intra prediction) environment, if the corresponding first color component block is encoded in the inter mode, the inter intra prediction may not be performed.

For example, if the coding mode of the corresponding block is an inter mode, inter color intra prediction may be performed. Here, a flag indicating whether inter-color intra prediction is performed may be signaled. Based on the flag, inter prediction or inter color intra prediction may be performed for the target block for prediction.

For example, if the intra prediction mode of the corresponding block corresponds to a predetermined mode, inter-color intra prediction may be performed.

For example, it may be determined whether to perform inter-color intra prediction according to CBF information on at least one of the corresponding block and neighboring blocks.

In the operation of predicting the second color component using the first color component, the size of the first color component block may be reconstructed so as to equalize the sizes of the first color component block or the second color component block. For example, if the color space of the image is YCbCr and the ratio between the color components is one of 4:4:4, 4:2:2, and 4:2:0, the block size may be different for the color components, and the blocks may be reconstructed to equalize the block sizes. Here, the reconstructed block may include at least one of a sample point of the corresponding block of the first color component and a reference sample point of the neighboring block.

For example, if the first color component block and the second color component block are equal in size, the reconstruction process may not be performed.

For example, if the size of the first color component block is larger than the size of the second color component block, the size of the first color component block may become equal to the size of the second color component block by downsampling the first color component block.

For example, if the size of the first color component block is smaller than the size of the second color component block, the size of the first color component block may become equal to the size of the second color component block by upsampling the first color component block.

In the reconstruction process, a filter may be applied to one or more samples. For example, the filter may be applied to one or more samples included in at least one of the first color component corresponding block, a neighboring block of the corresponding block, the second color component target block, and a neighboring block of the target block.

In the reference sample point constructing step, an indicator corresponding to a predetermined line among the plurality of reference sample point lines may be signaled, and in the reconstructing step, reconstruction may be performed using the predetermined line corresponding to the signaled indicator.

In the reconstruction process, if at least one of the boundary of the second color component prediction target block or the boundary of the first color component corresponding block corresponding to the second color component prediction target block corresponds to the boundary of at least one of the picture, the slice, the parallel block, the CTU, and the CU, a different reconstruction reference sample may be selected and used. Here, the number of upper reference sample lines may be different from the number of left reference sample lines.

For example, if the upper boundary of the corresponding block of the first color component corresponds to one of the above boundaries, the reconstruction may be performed using only the left reference sample, without using the upper reference sample. Alternatively, only one line of upper reference points may be used.

For example, if the left boundary of the corresponding block of the first color component corresponds to one of the above boundaries, the reconstruction may be performed using only the upper reference sample, without using the left reference sample.

For example, whether or not the boundaries match, reconstruction may be performed using N or M upper or left reference sample lines of the corresponding block of the first color component. For example, as shown in (a) of fig. 25, reconstruction may be performed using four upper reference sample lines and four left reference sample lines.

For example, if the upper boundary or the left boundary of the corresponding block of the first color component corresponds to one of the above boundaries, the number of upper reference sample lines used may be different from the number of left reference sample lines used. For example, as shown in (b) of fig. 25, reconstruction may be performed using two upper reference sample lines and four left reference sample lines of the corresponding block of the first color component. Alternatively, as shown in (c) of fig. 25, reconstruction may be performed using one upper reference sample line and two left reference sample lines of the corresponding block of the first color component.

In the reconstruction process, the horizontal length and the vertical length of the reference sample point of the first color component may not exceed the horizontal length and the vertical length of the corresponding block of the first color component. For example, as shown in (d) of fig. 25, reconstruction may be performed using one or more reference samples that do not exceed the horizontal length and the vertical length of the corresponding block of the first color component.

In the reconstruction process, the reference samples of the first color component may be reconstructed in different ways according to at least one of the size, shape and encoding parameters of at least one of the first color component corresponding block, the neighboring blocks of the first color component corresponding block, the second color component target block and the neighboring blocks of the second color component target block.

For example, for a corresponding block of the first color component or a neighboring block, the reference samples may be reconstructed using samples of the block whose mode is intra-coded, without using samples of the block whose coding mode is inter-coded.

For example, the reference samples of the first color component may be reconstructed in different ways according to the intra prediction modes of the corresponding blocks of the first color component.

For example, the reference samples of the first color component may be reconstructed in different ways based on quantization parameters of at least one of the corresponding block or neighboring blocks of the first color component.

For example, if the second color component corresponding block is shaped as a rectangle, reconstruction may be performed using reference samples adjacent to the square into which the first color component corresponding block is shaped.

The one or more prediction parameters may be derived using at least one of the reconstructed reference points of the respective blocks of the first color component and the reconstructed reference points of the respective blocks of the second color component. Hereinafter, the first color component and the first color component block may refer to the reconstructed first color component and the reconstructed first color component block, respectively.

Fig. 26 is a diagram depicting an embodiment of a corresponding block of a first color component reconstructed in the case where the size of a second color component prediction target block is 4×4. Here, the number of reference sample lines may be N, which may be 0 or an integer equal to or greater than 1.

As shown in (a) of fig. 26, the prediction parameters may be derived using the upper and left reference samples of the reconstructed first or second color component block. For example, the prediction parameters may be derived by adaptively using reference samples of the first color component reconstructed based on the intra prediction mode of the corresponding block of the first color component. Here, the reference samples of the second color component may also be adaptively used based on the intra prediction mode of the corresponding block of the first color component.

For example, if the intra prediction mode is a non-directional mode (such as a DC mode or a planar mode), as shown in (a) of fig. 26, an upper reference sample and a left reference sample of a corresponding block of the first color component may be used.

For example, if the intra prediction mode is a direction mode using all of the upper reference samples and the left reference samples, as shown in (a) of fig. 26, the upper reference samples and the left reference samples of the corresponding block of the first color component may be used.

For example, if the intra prediction mode is a direction mode using an upper reference sample, as shown in (b) or (c) of fig. 26, an upper reference sample of a corresponding block of the first color component may be used.

For example, if the intra prediction mode is a direction mode using a left reference sample, as shown in (d) or (e) of fig. 26, a left reference sample of a corresponding block of the first color component may be used.

For example, the prediction parameters may be derived by adaptively using reference samples of the first color component or the second color component according to at least one of the size or shape of the first color component or the second color component.

For example, if the size of the second color component target block corresponds to a predetermined size, the reference sample point of the first color component block or the second color component block may be adaptively used. For example, if the size of the second color component target block is 64×64, as many reference samples as at least one of 32, 16, and 8 of the upper reference sample or the left reference sample of the first color component block or the second color component block may be used.

For example, if the second color component target block is shaped as a rectangle, a reference sample point adjacent to the longer between latitude and longitude of the rectangle may be used. For example, if the shape of the target block is 32 x 8, then an upper reference sample of the first color component block or the second color component block may be used.

For example, if the second color component target block is shaped as a rectangle, then the reference points of a square block may be used. For example, if the shape of the target block is 32×8, reference samples adjacent to the 32×32 block may be used.

The reconstructed reference samples of the first color component block and the reconstructed reference samples of the second color component block may be used to derive prediction parameters and perform inter-color prediction. For example, the prediction parameter may be derived based on at least one of correlation, variation, mean, and distribution between reference samples of the color component, and may be derived using at least one method such as LS (least squares) and LMS (least mean squares), for example.

For example, the prediction parameters may be derived using the LMS method. Here, the prediction parameters may be a and b, or at least one of alpha and beta. For example, one can pass through the following [ equation 14 ] ]To derive a prediction parameter that minimizes the error between the first color component reference sample and the second color component reference sample. In [ equation 14]]In (2), p _n Reference sample points, p1', which may represent a second color component' _n The reconstructed reference sample point of the first color component may be represented. Furthermore, N may represent the number of horizontal reference points or vertical reference points used, and a and b may represent the prediction parameters.

[ equation 14]

The correlation between the reference samples can be calculated by equation 15. In equation 15, bitDepth may represent the bit depth.

[ equation 15]

k＝Max0,BitDepth+log2(N)-15)

Fig. 27 is an exemplary diagram depicting a sample of a first color component and a sample of a second color component. In fig. 27, p2 may represent a sample of the second color component and p1' may represent a reconstructed sample of the first color component.

For example, when there is a region without reference samples, the prediction parameters may be derived using only the existing reference samples.

Alternatively, default prediction parameters may be used without deriving the prediction parameterization from the reference samples. The default prediction parameters may be predefined, e.g., a may be 1 and b may be 0. Alternatively, the derived prediction parameters may be encoded/decoded.

For example, in inter-color prediction between Y, cb and Cr, prediction parameters for predicting Cb and Cr, respectively, may be derived from Y. Alternatively, the prediction parameters for predicting Cr may be derived from Cb. Alternatively, cb may be predicted using the prediction parameters derived from Y without deriving the prediction parameters for predicting Cr.

One or more prediction parameters may be derived. For example, one prediction parameter may be derived from a reference sample point for deriving the prediction parameter and whose value satisfies a predetermined condition. Furthermore, another prediction parameter may be derived from reference samples that do not satisfy the predetermined condition.

The prediction parameters may be derived from prediction parameters of one or more blocks adjacent to the target block for prediction. For example, if a neighboring block is encoded by inter-color prediction, a prediction parameter for inter-color prediction may be used as a prediction parameter for a predicted target block. Here, at least one of whether a neighboring prediction parameter has been used, location information about the neighboring block, and a prediction parameter index may be signaled.

Inter-color intra prediction may be performed using at least one of the derived prediction parameters. For example, prediction may be performed on the second color component target block by applying the derived prediction parameters to the reconstructed signal of the reconstructed first color component according to [ equation 16 ].

[ equation 16]

p2[x,y]＝a×p1′[x,y]+d

Alternatively, prediction may be performed on the second color component target block by applying the derived prediction parameters to the reconstructed residual signal of the first color component according to [ equation 17 ].

[ equation 17]

p2[x,y]＝p2_pred[x,y]+a×p1′_residual[x,y]

In equation 17, a may represent the derived prediction parameter, and p1' _residual may represent the residual signal of the first color component. Further, p2_pred may represent a signal obtained by predicting the second color component target block using at least one of a non-directional intra prediction mode or a directional intra prediction mode.

If one or more prediction parameters are derived, the one or more prediction parameters may be applied to the reconstructed samples of the first color component. For example, if the reconstructed samples of the first component satisfy a predetermined condition, inter-color intra prediction may be performed by applying a prediction parameter derived from samples satisfying the predetermined condition. Alternatively, if the reconstructed samples of the first component do not meet the predetermined condition, inter-color intra prediction may be performed by applying prediction parameters derived from samples that do not meet the predetermined condition.

The intra encoding/decoding process may be performed for each of the luminance signal and the chrominance signal. For example, in the intra encoding/decoding process, at least one of deriving an intra prediction mode, dividing a block, constructing a reference sample, and performing intra prediction may be differently applied for a luminance signal and a chrominance signal.

The intra encoding/decoding process may be equally performed for the luminance signal and the chrominance signal. For example, at least one of deriving an intra prediction mode in an intra encoding/decoding process applied to a luminance signal, dividing a block, constructing a reference sample, and performing intra prediction may be equally applied to a chrominance signal.

The method may be performed in the same way in the encoder and decoder. For example, in the intra encoding/decoding process, at least one of applying the derived intra prediction mode, dividing the block, constructing the reference samples, and performing the intra prediction may be equally applied in the encoder and decoder. Furthermore, the order in which the methods are applied may be different in the encoder and decoder. For example, in an operation of performing intra encoding/decoding with respect to a current block, an encoder may encode an intra prediction mode determined by performing at least one intra prediction after constructing a reference sample.

Embodiments of the present invention may be applied according to the size of at least one of the encoded block, the prediction block, the block, and the unit. Here, the size may be defined as a minimum size and/or a maximum size in order to apply the embodiment, and may be defined as a fixed size to which the embodiment is applied. Further, the first embodiment may be applied in a first size and the second embodiment may be applied in a second size. That is, the embodiment may be applied multiple times according to the size. Furthermore, the embodiments of the present invention may be applied only when the size is equal to or greater than the minimum size and equal to or less than the maximum size. That is, the embodiment may be applied only when the block size is in a predetermined range.

For example, the embodiment can be applied only when the size of the encoding/decoding target block is equal to or larger than 8×8. For example, the embodiment can be applied only when the size of the encoding/decoding target block is equal to or larger than 16×16. For example, the embodiment can be applied only when the size of the encoding/decoding target block is equal to or larger than 32×32. For example, the embodiment can be applied only when the size of the encoding/decoding target block is equal to or larger than 64×64. For example, the embodiment may be applied only when the size of the encoding/decoding target block is equal to or greater than 128×128. For example, the embodiment can be applied only when the size of the encoding/decoding target block is 4×4. For example, the embodiment can be applied only when the size of the encoding/decoding target block is equal to or smaller than 8×8. For example, the embodiment can be applied only when the size of the encoding/decoding target block is equal to or smaller than 16×16. For example, the embodiment can be applied only when the size of the encoding/decoding target block is equal to or greater than 8×8 and equal to or less than 16×16. For example, the embodiment can be applied only when the size of the encoding/decoding target block is equal to or greater than 16×16 and equal to or less than 64×64.

Embodiments of the present invention may be applied according to temporal layers. An identifier for identifying a temporal layer to which an embodiment may be applied may be signaled and an embodiment may be applied for the temporal layer indicated by the indicator. Here, the identifier may be defined to indicate a minimum layer and/or a maximum layer to which an embodiment may be applied, and may be defined to indicate a specific layer to which an embodiment may be applied.

For example, the embodiment may be applied only when the temporal layer of the current picture is the lowest layer. For example, the embodiment may be applied only when the temporal layer identifier of the current picture is 0. For example, the embodiment may be applied only when the temporal layer identifier of the current picture is equal to or greater than 1. For example, the embodiment may be applied only when the temporal layer of the current picture is the highest layer.

As described in the embodiments of the present invention, the reference picture set used in the process of reference picture list construction and reference picture list modification may use at least one of reference picture lists L0, L1, L2, and L3.

According to an embodiment of the present invention, at least one up to N motion vectors of the encoding/decoding target block may be used when the deblocking filter calculates the boundary strength. Here, N indicates a positive integer equal to or greater than 1, such as 2, 3, 4, and the like.

In motion vector prediction, an embodiment of the present invention may be applied when a motion vector has at least one of the following units: a 16-pixel (16-pel) unit, an 8-pixel (8-pel) unit, a 4-pixel (4-pel) unit, an integer-pixel (integer-pel) unit, a 1/2-pixel (1/2-pel) unit, a 1/4-pixel (1/4-pel) unit, a 1/8-pixel (1/8-pel) unit, a 1/16-pixel (1/16-pel) unit, a 1/32-pixel (1/32-pel) unit, and a 1/64-pixel (1/64-pel) unit. Further, in performing motion vector prediction, a motion vector may be optionally used for each pixel unit.

The type of the strip to which the embodiments of the present invention are applied may be defined and the embodiments of the present invention may be applied according to the type of the strip.

For example, when the slice type is T (three-way prediction) -slice, the prediction block may be generated by using at least three motion vectors, and may be used as a final prediction block of the encoding/decoding target block by calculating a weighted sum of the at least three prediction blocks. For example, when the slice type is Q (four-way prediction) -slice, the prediction block may be generated by using at least four motion vectors, and may be used as a final prediction block of the encoding/decoding target block by calculating a weighted sum of at least four prediction blocks.

The embodiments of the present invention can be applied to inter prediction and motion compensation methods using motion vector prediction and inter prediction and motion compensation methods using skip mode, merge mode, and the like.

The shape of the block to which the embodiments of the present invention are applied may have a square shape or a non-square shape.

In the above-described embodiment, the method is described based on a flowchart having a series of steps or units, but the present invention is not limited to the order of the steps, and some steps may be performed simultaneously with other steps or may be performed in a different order from other steps. Furthermore, it will be understood by those of ordinary skill in the art that steps in the flowcharts are not mutually exclusive, and other steps may be added to the flowcharts, or some steps may be deleted from the flowcharts without affecting the scope of the present invention.

Embodiments include various aspects of the examples. All possible combinations for the various aspects may not be described, but one of ordinary skill in the art will be able to recognize different combinations. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.

The embodiments of the present invention can be implemented in the form of program instructions executable by various computer components and recorded on a computer-readable recording medium. The computer readable recording medium may include individual program instructions, data files, data structures, etc., or a combination of program instructions, data files, data structures, etc. The program instructions recorded in the computer-readable recording medium may be specially designed and constructed for the present invention, or they may be known to those skilled in the art of computer software technology. Examples of the computer-readable recording medium include: magnetic recording media (such as hard disks, floppy disks, and magnetic tape); an optical data storage medium (such as a CD-ROM or DVD-ROM); magneto-optical media (such as floppy disks); and hardware devices that are specially constructed for storing and carrying out the program instructions (e.g., read-only memory (ROM), random Access Memory (RAM), flash memory, etc.). Examples of program instructions include not only machine language code, which is formed by a compiler, but also high-level language code that may be implemented by a computer using an interpreter. The hardware devices may be configured to be operated by one or more software modules to perform the processes according to the invention, and vice versa.

Although the present invention has been described in terms of specific terms (such as detailed elements) and limited embodiments and figures, they are merely provided to facilitate a more general understanding of the present invention, and the present invention is not limited to the above-described embodiments. Those skilled in the art to which the invention pertains will appreciate that various modifications and variations may be made from the foregoing description.

The spirit of the invention should, therefore, not be limited to the above-described embodiments, and the full scope of the appended claims and equivalents thereof should be accorded the full scope of the invention.

Industrial applicability

The present invention can be used for encoding/decoding an image.

Claims

1. A method of decoding video, the method comprising:

obtaining a current block by dividing an image;

determining an intra prediction mode of the current block;

determining a reference sample line of the current block from a plurality of reference sample lines;

deriving a reference sample point of the current block from the selected reference sample point line;

generating a prediction block by performing intra prediction with respect to the current block;

obtaining a residual block of the current block by performing inverse transform with respect to the current block; and

reconstructing the current block by adding the prediction block and the residual block,

Wherein, among the plurality of reference sample lines, the reference sample line of the current block is determined based on whether the upper boundary of the current block corresponds to the boundary of the encoding tree block.

2. The method of claim 1, wherein only quadtree partitioning is available for the encoded block in case that a size of the encoded block is greater than a predetermined size, the current block being the encoded block or a leaf node encoded block generated by partitioning the encoded block.

3. The method of claim 1, wherein the intra-prediction mode of the current block is determined by an intra-prediction mode candidate derived based on an intra-prediction mode of a left neighboring block that is a block adjacent to a lower left side of the current block and an intra-prediction mode of an upper neighboring block that is a block adjacent to an upper right side of the current block.

4. The method of claim 3, wherein the intra prediction mode candidate is derived by using a maximum value and a minimum value of intra prediction modes of the left neighboring block and intra prediction modes of the upper neighboring block.

5. The method of claim 1, wherein, among the plurality of reference sample lines, a reference sample line used to derive the reference sample point is determined based on information decoded from a bitstream.

6. The method of claim 1, wherein the method further comprises: the reference sample point is filtered and,

wherein the filtering of the reference sample points is performed only when a first one of the plurality of reference sample points is determined as the reference sample point of the current block.

7. The method of claim 1, wherein the intra prediction is performed by applying a filter to reference samples,

wherein the type of the filter is differently determined according to which reference sample line of the plurality of reference sample lines is determined as the reference sample line of the current block.

8. The method of claim 1, wherein availability of samples outside a predetermined range for samples in the plurality of reference sample lines is not checked and samples outside the predetermined range are replaced with neighboring samples within the predetermined range.

9. A method of encoding video, the method comprising:

obtaining a current block by dividing an image;

determining an intra prediction mode of the current block;

obtaining a residual block by subtracting the prediction block from the original block; and

a transform is performed on the residual block,

10. A bit stream transmission method of transmitting a bit stream, the bit stream transmission method comprising:

generating a bitstream by an image encoding method; and

the bit stream is transmitted in a manner such that,

the image coding method comprises the following steps:

obtaining a current block by dividing an image;

determining an intra prediction mode of the current block;

a transform is performed on the residual block,